UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL   EXPERIMENT   STATION 

BERKELEY,    CALIFORNIA 


MONILIA  BLOSSOM  BLIGHT  (BROWN  ROT) 

OF  APRICOTS 


BY 

B.  A.  RUDOLPH 


BULLETIN  No.  383 

February,  1925 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1925 


MONILIA  BLOSSOM  BLIGHT  (BROWN  ROT)  OF  APRICOTS* 

By  B.  A.  RUDOLPH 


CONTENTS 

PAGE 

Summary 4 

Introductory 7 

The  Disease:   Its  characteristics  and  its  cause 7 

History  of  the  disease 15 

Importance  of  the  disease  in  California 18 

Possible  reasons  for  the  increase  of  the  disease  in  California 18 

Experiments  for  the  control  of  Monilia  blossom  blight 19 

Introductory  statement 19 

Scope  of  the  experiments 19 

The  time  the  sprays  were  applied 20 

The  number  of  trees  used  in  the  experiments 20 

How  the  sprays  were  applied 20 

Method  of  determining  results 20 

Observations  made  in  private  orchards 21 

Explanation  of  terms 21 

Dormant  sprays 23 

Experimental 23 

Results  obtained  in  private  orchards  with  dormant  sprays 23 

Delayed  dormant  and  red  bud  sprays 23 

Successful  results  obtained  in  private  orchards 23 

Unsuccessful  results  obtained  in  private  orchards 24 

Results  obtained  experimentally  with  red  bud  sprays 24 

The  most  favorable  period  for  securing  good  results  with  one  spray 26 

Bloom  sprays 28 

Experimental 28 

Results  obtained  with  full  bloom  sprays  in  private  orchards 28 

Spraying  before  the  full  bloom.     Results  obtained  in  private  orchards 28 

Multiple  spraying 30 

Multiple  spraying  in  the  pre-bloom  period 31 

Multiple  spraying  throughout  the  susceptible  period 32 

Discussion - 34 

Reasons  for  the  failure  of  single  sprays  to  control  the  disease 34 

Reasons  for  the  failure  of  dormant  sprays  to  control  the  disease 34 

Reasons  for  the  failure  of  full  bloom  sprays  to  control  the  disease 34 

Conditions  under  which  red  bud  sprays  succeed 35 

Reasons  for  the  success  of  the  multiple  spray  treatment 35 

*  The  term  Monilia  blossom  blight  is  suggested  for  adoption  as  a  common 
name  for  the  blossom  and  the  twig  blight  phase  of  the  disease  to  distinguish 
it  from  "Brown  Rot,"  a  decay  of  the  ripening  fruit,  produced  by  the  same 
organism.     The  term  brown  rot  is  so  universally  used   elsewhere  to  designate 

the  rot  of  the  fruit  that  its  use  in  California  to  designate  the  disease  of  the 
blossoms  and  twigs  is  very  confusing. 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

PAGE 

Orchard  sanitation 35 

The  relation  of  careful  pruning  to  spraying  in  the  control  of  the  disease 35 

Ordinary  pruning  better  than  no  pruning 38 

The  practicability  of  careful  pruning 38 

The  disposal  of  infectious  material 38 

Experiments  to  produce  the  apothecial  form 38 

Depleted  vigor  of  the  trees  conducive  to  Monilia  blossom  blight r39 

The  relation  of  organic  fertilizers  to  the  propagation  of  the  brown  rot  fungus. .  39 

Ornamental  plants  as  "carriers"  of  the  brown  rot  fungus 39 

Fungicides 40 

Bordeaux  mixture 40 

Sulfur-containing  compounds 41 

Lime-sulfur  damage 41 

Effect  of  pure  sulfur  on  ripening  apricots 42 

Oil  sprays 43 

Value  as  dormant  sprays 43 

Red  bud  oil  sprays 44 

Fungicidal  dusts 44 

Experimental  dusting  for  the  control  of  the  disease 44 

Results  obtained  with  fungicidal  dusts  in  private  orchards 46 

When  to  spray  for  Monilia  blossom  blight  control 46 

The  preparation  of  Bordeaux  mixture 47 

The  preparation  of  the  stock  solutions 47 

How  to  mix  the  spray 48 

Commercially  prepared  Bordeaux  sprays 49 

Bibliography 50 


SUMMARY 

Monilia  blossom  blight  is  due  to  the  attack  of  a  fungus  of  the  genus 
Sclerotinia.  The  fungus  reproduces  itself  by  means  of  spores  which 
are  produced  in  abundance,  before  the  blossoms  open,  on  the  old 
blighted  twigs  and  decayed  fruits  left  in  the  trees.  A  second  reproduc- 
tive form  is  known,  but  it  rarely  occurs  in  California, 

The  blossoms  may  be  attacked  at  any  time  after  the  buds  have 
cracked  and  show  the  folded  white  petals  beneath  the  red  sepals,  until 
the  full  bloom  or  even  a  little  later  when  the  petals  have  been  shed. 
Having  killed  a  blossom  the  fungus  passes  into  the  twig  and  kills  it. 
Later  the  fungus  attacks  the  ripening  fruit  producing  a  characteristic 
"brown  rot. n 

The  disease  was  first  described  in  Europe  in  1796,  in  America  in 
1881,  and  it  was  known  to  exist  in  California  before  1900. 

The  disease  has  become  exceedingly  destructive  in  California  in 
recent  years.  This  is  possibly  due  to  the  planting  of  less  resistant 
varieties. 


Bulletin  383]  BROWN  ROT  OF  APRICOTS  5 

Over  one  hundred  different  treatments,  involving  the  use  of  most 
of  the  better  known  fungicides,  oil  emulsions,  coal-tar  derivative 
sprays,  fungicidal  dusts  and  various  proprietary  preparations  pre- 
sumably possessing  fungicidal  properties,  have  been  tried  out  experi- 
mentally during  the  past  four  years  for  the  control  of  the  disease. 
These  materials  were  used  separately  or  in  combination,  in  single  or 
multiple  applications  at  various  times  either  before,  during  or  after 
the  bloom.  In  addition  to  these  experiments,  records  of  the  methods 
employed  and  the  control  obtained  in  approximately  two  hundred 
private  orchards  were  compiled.  From  the  data  accumulated  it  has 
been  concluded  that : 

(1)  In  orchards  already  seriously  infected  and  situated  in  localities 
where  normal  climatic  conditions  render  the  disease  difficult  to  con- 
trol, a  dormant  spray  of  any  standard  fungicide  may  decrease  the 
amount  of  disease  noticeably,  but  seldom  sufficiently  to  be  of  practical 
value. 

(2)  A  spray  applied  in  the  spring  when  the  buds  are  expanding, 
or  still  later  in  the  red  bud  stage,  affords  the  best  control  obtainable 
with  any  one  spray.  Frequently  such  a  spray  controls  the  disease. 
In  orchards  situated  in  localities  normally  damp  during  the  susceptible 
period  and  where  little  effort  has  been  made  to  remove  the  great  accu- 
mulation of  old  infectious  material  from  the  trees,  the  control  obtained 
by  such  a  spray  may  be  entirely  unsatisfactory,  although,  relatively 
speaking,  the  amount  of  disease  may  be  much  diminished. 

(3)  The  more  closely  the  application  of  the  spray  approximates  the 
period  when  the  buds  are  cracking,  showing  the  folded  white  petals 
beneath  the  red  sepals,  the  greater  the  control  is  apt  to  be,  but  there  is 
no  certainty  that,  even  at  this  favorable  period,  one  application  of  any 
fungicide  will  give  a  practical  control  of  the  disease  under  adverse 
conditions.  Relatively  speaking,  the  control  will  be  greater  at  this 
time  than  at  any  other,  but  from  the  practical  standpoint,  it  is  likely 
to  be  a  failure. 

(4)  A  spray  applied  at  any  time  after  the  blossoms  are  open 
usually  affords  some  relief,  but  from  the  practical  standpoint,  the 
control  afforded  generally  is  a  failure,  and,  the  longer  the  spray  is 
delayed,  the  greater  the  failure  is  likely  to  be.  Similarly,  a  full  bloom 
spray  usually  affords  some  relief,  but  the  results  are  invariably  very 
unsatisfactory  from  the  practical  standpoint  and  particularly  so  if  the 
susceptible  period  is  damp. 

(5)  All  sprays  may  help  a  little  regardless  of  the  time  of  appli- 
cation. 


6  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

(6)  Regardless  of  whether  or  not  the  trees  have  been  sprayed, 
there  will  be  little  or  no  disease  even  though  the  fungous  spores  are 
present  in  the  greatest  abundance,  unless  rain,  heavy  dew  or  fog  occurs 
during  the  susceptible  period.  Moisture  is  the  great  determining 
factor  in  the  infection  of  the  flowers.  Many  growers  not  recognizing 
this  fact  credit  the  control  of  the  disease  in  dry  seasons  to  weak 
mixtures  of  standard  fungicides  or  to  other  spray  materials  which 
under  more  normal  conditions  prove  utterly  unsuited  to  the  purpose. 

(7)  In  badly  diseased  orchards  situated  in  localities  which  are 
favorable  to  the  ready  development  of  the  disease  because  the  weather 
is  normally  humid  during  the  blossoming  period,  and  in  cases  where 
little  or  no  attempt  has  been  made  to  remove  the  great  accumulation  of 
old  infectious  material  from  the  trees,  multiple  spraying  throughout 
the  entire  susceptible  period  is  the  only  means  likely  to  secure  a  prac- 
tical control.  AVith  this  method  several  sprays  are  applied,  starting 
with  the  red  bud  spray  and  following  with  others  in  quick  succession 
as  the  flowers  continue  to  open  until  the  trees  have  reached  full  bloom, 
or  even  a  little  later  when  the  petals  have  been  shed. 

(8)  The  degree  of  control  in  badly  diseased  orchards  is  propor- 
tionate to  the  number  of  sprays  applied  during  the  susceptible  period 
of  the  blossoms. 

(9)  Orchard  sanitation  (the  careful  removal  of  all  infectious 
material  from  the  trees  and  the  ground)  is  as  vital  as  spraying  in  the 
control  of  the  disease,  but  should  be  regarded  as  an  auxiliary  to  spray- 
ing operations,  rather  than  as  a  separate  means  of  controlling  the 
disease. 

(10)  The  extent  of  the  control  by  sprays  is  largely  affected  by  the 
degree  to  which  orchard  sanitation  has  been  observed. 

(11)  Manures,  decaying  and  freshly  cut  grasses  and  alfalfa  in  the 
orchard  do  not  harbor  the  fungus  over  winter.  Many  ornamental 
plants  were  examined,  but  the  disease  was  found  only  in  the  Japanese 
quince  (Chaenomales  japonica). 

(12)  The  fungicide  best  adapted  to  use  on  apricot  trees  and  for  the 
control  of  the  disease  is  home-made  Bordeaux  8-8-50.  Bordeaux 
5-5-50  or  6-6-50  frequently  gives  excellent  results  in  orchards  less 
severely  affected  or  situated  in  localities  where  climatic  conditions  are 
more  favorable  to  the  control. 

(13)  Bordeaux  does  not  interfere  with  the  fertilization  of  the 
apricot  blossoms  whatever  the  time  of  application,  fertilization  appar- 
ently taking  place  before  the  red  buds  open. 


Bulletin  383]  BROWN  ROT  OF  APRICOTS  7 

(14)  Having  brought  the  disease  within  the  limits  of  practical 
control  by  the  multiple  spray  method,  fewer  sprays,  and  in  most 
instances,  only  one  spray  of  Bordeaux  8-8-50  or  weaker  strength  will 
be  needed  in  succeeding  years  to  hold  the  disease  in  check. 

(15)  Lime-Sulfur,  Soda-Sulfur  and  other  sulfur-containing  com- 
pounds are  distinctly  unsuited  for  use  on  apricots  because  they  cause 
a  physiological  injury  to  the  trees  commonly  referred  to  as  "sulfur 
poisoning. '  The  foliage  on  such  trees  is  stunted  and  yellowish,  the 
fruit  is  dwarfed,  of  poor  color  and  quality,  and  ripens  late.  Even  pure 
sulfur  applied  with  water  to  the  ripening  fruit  may  cause  it  to  be 
stunted  and  late  in  ripening.  Apricot  trees  treated  with  sulfur  or 
sulfur-containing  compounds  sometimes  fail  to  bloom  the  following 
season. 

(16)  The  more  commonly  used  oil  emulsions,  miscible  oils  and 
coal-tar  derivative  sprays  which  are  applied  in  winter  for  the  control 
of  insect  pests  have  some  fungicidal  effect,  but  insufficient  for  the 
control  of  the  disease  in  badly  diseased  orchards  in  humid  localities. 
The  relative  degree  of  control  they  afford  is  sometimes  quite  marked, 
but  from  the  practical  standpoint  they  are  generally  unsatisfactory. 
Applied  in  the  spring  they  usually  burn  the  buds  or  lower  the  crop 
yield  by  interfering  with  the  pollination  of  the  flowers. 

(17)  Fungicidal  dusts  are  ineffective  in  the  control  of  the  disease, 
particularly  in  orchards  in  localities  where  the  disease  is  difficult  to 
control.  Thirteen  different  fungicidal  dusts  were  used  in  single  and 
multiple  applications  throughout  the  susceptible  period,  but  none  were 
found  equal  to  a  single  application  of  liquid  Bordeaux  under  similar 
conditions.  Generally  the  results  obtained  from  the  dusts  were  very 
poor  from  both  the  relative  and  practical  standpoints. 


INTRODUCTORY 

THE  DISEASE :    ITS  CHABACTEKISTICS  AND  ITS  CAUSE 

Monilia  blossom  blight  (brown  rot)  is  due  to  the  attack  of  a  fungus 
of  the  genus  Sclerotinia. 

This  fungus  has  two  reproductive  forms,  the  imperfect  stage 
(Monilia)  and  the  perfect  (Sclerotinia).  The  latter  stage  is  exceed- 
ingly rare  in  California,  the  former  very  common. 

Monilia  blossom  blight  never  kills  a  tree ;  it  is  primarily  a  disease 
of  the  second-year  or  fruit  wood  which  it  attacks  through  the  blossoms. 


8 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


The  severity  of  the  attack  depends  on  the  weather.  In  climates 
favorable  to  the  disease  its  severity  increases  yearly  if  not  controlled. 

In  the  spring-  the  apricot  blossoms  are  attacked  at  any  time  after 
the  buds  have  cracked  and  show  the  folded  white  petals  beneath  the 
red  sepals  until  the  petals  have  fallen.  The  killed  flowers  remain 
fixed  to  the  twigs  until  eventually  dislodged  by  storms. 


> 


Fig.  1. — Apricot  fruit  spurs  killed  by  Monilia  blossom  blight.  The  dead 
flowers  do  not  fall  off.  Note  the  production  of  gum  at  the  junction  of  living  and 
dead  tissue.     From  Bull.  326,  Calif.  Agr.  Exp.  Sta. 


From  the  flowers  the  fungus  passes  into  the  spurs,  killing  them 
back  as  much  as  five  inches  in  one  week  and  a  foot  or  more  before  it 
ceases  to  be  active.  Fruiting  twigs  may  be  killed  back  five  feet  by 
numerous  infections  along  their  entire  length  or  by  girdling  from  a 
single  infection  at  the  base. 


Bulletin  383] 


BROWN    ROT    OF    APRICOTS 


9 


Copious  amounts  of  amber-  or  honey-colored  gum  are  character- 
istically produced  at  the  junction  of  the  living  and  the  dead  tissue. 
It  is  harmless  and  being  readily  soluble  in  rain  water  may  not  always 
be  present.     (Fig.  1.) 

In  humid  weather  the  dying  flower  parts  usually  become  covered 
with  fungous  spores  (the  Monilia  stage)  within  about  twenty-four 
hours  after  infection. 


Fig.  2. — Production  of  Monilia  spores  from  cankers  on  almond  twigs  killed 
the  previous  spring  by  Monilia  blossom  blight.  The  spore  pustules  are  recog- 
nized as  roundish  light-colored  bodies.  Natural  size.  Prom  Bull.  326,  Calif. 
Agr.  Exp.  Sta. 


Having  killed  a  spur  the  fungus  becomes  dormant  or  inactive 
until  the  following  winter  when  it  is  reactivated  by  wet  weather. 
Spores  are  produced  in  almost  inconceivable  numbers  on  the  dead 
wood.  (Fig.  2.)  If  the  wood  dries  out,  spore  production  ceases  for 
the  time  being. 


10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Spores  are  reproductive  bodies.  The  Monilia  spores  are  produced 
in  chains.  Hundreds,  possibly  thousands  of  these  spore  chains  are 
grouped  in  dense  clusters,  visible  as  tiny  powdery  pustules  or  cushions 
on  the  old  decayed  fruits  and  twigs.  At  first  the  pustules  are  bluish- 
or  ash-gray,  becoming  buff  to  brown  as  they  age  and  dry  out.  When  a 
spore  is  ripe  it  falls  away  from  the  chain,  and  new  ones  are  constantly 
being  produced  from  the  base.     (Fig.  3.) 


y 


r\ 


Mi- 

IP 


Fig.  3. — Photomicrograph  of  Monilia  spores  produced  in  culture  on  Ciapeck  agar. 


A  spore  germinates  if  sufficient  moisture  is  present  and  sends 
forth  a  fungous  thread  which  quickly  penetrates  and  kills  the  petals 
and  reproductive  flower  parts,  finally  passing  into  the  spur. 

Large,  ugly  cankers  may  be  produced  in  the  older  wood,  the  attack 
usually  being  made  from  the  base  of  a  killed  spur.  The  cankers 
ordinarily  are  inconspicuous  until  the  bark  dries  and  peels  away  in 
summer  revealing  deep  gummy  lesions.  These  ordinarily  heal  over  by 
the  end  of  the  year  and  cause  no  further  trouble. 

New  tender  foliage  may  be  attacked  in  very  wet  weather,  but  the 
resistance  of  the  new  growth  to  the  disease  is  usually  marked. 

Repealed  efforts  to  induce  the  fungus  to  attack  healthy  bark  of 
either  first  or  second  year  wood  by  binding  spore  pustules  or  spore 
covered  fruits  to  the  twigs  with  moist  bandages  failed. 


Bulletin  383] 


BROWN    ROT    OF    APRICOTS 


11 


Occasionally,  in  very  wet  weather  the  young  fruits  in  the  jackets 
are  attacked,  but  after  the  old  flower  parts  have  fallen  away  they 
rarely  suffer  much.  Attacks  at  this  stage  are  usually  made  through 
insect  wounds  and  abrasions. 

A  rot  of  small  green  apricots  produced  by  Sclerotinia  libertiana 
Fcl.,  a  closely  related  fungus,  is  frequently  confused  with  brown  rot. 


Fig.  4 — Brown  Eot  of  ripe  apricots.  The  disease  passes  from  fruit  to  fruit 
in  clusters,  through  the  skin.  Note  enormous  production  of  Monilia  spores  on 
the  surface.     Natural  size.     From  Bull.  218,  Calif.  Agr.  Exp.  Sta. 


12 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Ripe  fruit  is  much  less  resistant  to  brown  rot.  According  to 
Cordley,33  Smith,19  Cooley,69  Valleau77  and  others  the  fungus  can 
penetrate  the  healthy  skin  of  peaches,  plums  and  cherries,  and  the 
same  is  probably  true  of  the  apricot.  One  diseased  fruit  will  occasion 
the  destruction  of  an  entire  cluster  of  apricots,  the  fungus  passing 
through  the  skin  of  each  with  ease. 


Fig.  5. — Apricot  "mummy"  produced  by  Brown  Rot.  Spore  pustules  of  the 
fungus  may  be  clearly  seen  on  the  fruit  near  the  stem.  From  Bull.  326,  Calif. 
Exp.  Sta. 


Once  attacked,  the  green  or  ripe  fruit  rots  quickly.  A  minute, 
circular  brown  spot  appears  which  rapidly  enlarges,  finally  enveloping 
the  entire  fruit.  The  common  term  "brown  rot"  is  derived  from  the 
appearance  of  the  decay  of  the  fruit.  Fungus  spores  are  produced 
on  the  rotting  fruits  in  enormous  quantities.     (Pig.  4.) 

Most  affected  fruits  fall,  but  some  remain  in  the  trees  where  they 
shrivel  to  a  tough,  leathery  condition  and  as  such  are  known  as 
"mummies. "     (Fig.  5.) 


Bulletin  383] 


BROWN   ROT   OF   APRICOTS 


13 


From  the  old  mummies  on  the  ground,  the  so-called  apothecial  or 
perfect  stage  is  produced.  Hard,  irregular-shaped,  black  bodies,  some- 
what resembling  black  rubber  when  fresh  and  frequently  as  large  as 
a  grain  of  corn,  develop  in  the  decayed  fruit  tissue.    They  are  known 


Fig.  6. 


-Prune  "mummy"  with  apothecia  of  the  brown  rot  fungus. 
(Courtesy  C.  Brooks  and  D.  Fisher,  U.  S.  D.  A.) 


as  sclerotia  and  constitute  a  resting  stage.  In  this  form  the  fungus 
can  safely  withstand  the  cold  of  winter  and  the  heat  and  drought  of 
summer.  In  the  spring,  at  blossom  time,  apothecia  are  produced  from 
the  sclerotia.  They  are  little  fleshy  fungous  bodies,  trumpet-  or 
morning  glory-shaped,  which  consist  of  a  stalk  several  millimeters  to 


14 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 


several  inches  long  and  a  cup  or  trumpet-shaped  structure  at  the  top, 
two  or  three  millimeters  to  several  centimeters  in  diameter.     (Fig.  6.) 

Roberts95  and  Ezekiel96  have  shown  that  apothecia  may  be  produced 
in  the  spring  following  the  decay  of  the  fruit,  although  ordinarily 
they  do  not  appear  until  the  second  year. 

The  apothecia  are  lined  on  their  upper  or  inner  surface  with 
innumerable,  minute,  cylindrical  sacks  called  asci.  (Fig.  10.)  Each 
ascus  contains  eight  spores  which  are  released  when  ripe  and  carried 
by  air  currents  to  the  blossoms.     The  flowers  are  quickly  attacked  if 


Fig.  7. — Flowers  and  twigs  of  the  Japanese  Quince  (Chaenomeles  japonica) 
attacked  by  Monilia  blossom  blight.  Note  heavy  production  of  Monilia  spores 
on  the  dead  blossom.    Twice  natural  size. 


moisture  conditions  are  favorable,  and  within  a  day  or  two  the  dead 
and  dying  parts  become  covered  with  masses  of  spores  of  the  chain 
type  already  described.    Thus  the  cycle  is  complete. 

The  apothecial  stage  is  the  great  source  of  trouble  in  the  eastern 
states,  also  in  certain  parts  of  Oregon.  In  California  it  is  exceedingly 
rare  and  of  no  consequence  in  the  propagation  of  the  fungus.  Also, 
since  the  Monilia  stage  insures  abundant  reproduction  in  the  spring 
it  is  superfluous. 

Pollock84  has  shown  that  while  the  mummies  eventually  rot  away 
in  the  soil,  the  sclerotia  may  persist  there  for  ten  years  and  annually 
send  up  their  crop  of  spore-bearing  apothecia. 


Bulletin  383]  BROWN  ROT  OF  APRICOTS  15 


HISTOEY  OF  THE  DISEASE 

The  first  published  account  of  brown  rot  of  fruit  appeared  in  1796 
in  Europe  when  Persoon1  gave  the  name  Torida  fructigena  to  a  fungus 
which  he  found  on  decayed  fruit  of  Prunus  domestica  (European 
plum),  Amygdalus  persica  (peach)  and  Pyrus  communis  (French 
pear).  Many  investigators,  including  Albertini  and  Schweinitz,3 
Fuckel,12  Saccardo14  and  Rabenhorst10  have  used  this  name.  In  1801 
Persoon2  changed  the  name  of  the  fungus  to  Monilia  fructigena  which 
name  is  still  in  use.  In  1817  Kunze  and  Schmidt4  referred  the  fungus 
to  Oidium  fructigenum,  and  among  those  who  retained  this  name  are 
Ehrenberg,5  Fries,7  Duby,8  Cooke13  and  Smith.17  This  name,  however, 
has  now  gone  out  of  general  use.  In  1822  Persoon6  renamed  the  fungus 
again,  calling  it  Acrosporium  fructigenum,  a  classification  which  has 
never  been  accepted  by  scientific  writers.  In  1833  Wallroth9  referred 
the  fungus  to  both  Oospora  Candida  and  0.  fructigena,  but  in  1875  von 
Thiimen15  changed  the  name  to  Oidium  wallrothii  and  still  later  to 
0.  fructigenum. 

In  1851  Bonorden11  described  for  the  first  time  another  brown  rot 
fungus  occurring  ' '  on  rotting  fruit ' '  which  he  named  Monilia  cinerea. 
The  differences  between  this  fungus  and  the  one  described  by  Persoon 
were  considered  too  meager,  however,  by  some  investigators  to  permit 
of  its  being  regarded  as  a  distinct  species.  In  1898-99  Woronin32 
proved  that  the  two  species  are  distinct. 

In  1893  Schroter27  referred  the  two  species  of  Monilia  to  the  genus 
Sclerotinia,  being  confident  from  his  studies  of  them  that  a  second 
reproductive  form,  the  apothecial  stage  eventually  would  be  dis- 
covered. In  1904  Aderhold43  confirmed  these  predictions  when  he 
found  the  perfect  stage  of  Monilia  fructigena  in  Europe. 

In  the  United  States  brown  rot  has  been  very  troublesome,  and  for 
nearly  half  a  century  there  has  been  a  steady  output  of  publications 
dealing  with  the  pathological,  physiological,  morphological  and  etio- 
logical aspects  of  the  disease  and  its  therapeutics.  The  better  known 
papers  are  those  of  Peck16  (1881),  Arthur18  (1886),  E.  F.  Smith,19 
Galloway20  (1889),  Humphrey21  (1890),  Smith22  (1891),  Halsted,23 
Chester,24  Jones25  (1892),  Humphrey26  (1893),  Taft,28  Bailey29  (1894), 
Kinney,30  Goff31  (1987),  Cordley33  (1899),  Quaintance,34  Waugh,35 
Bioletti36  (1900),  Norton,37  Clinton,38  Bioletti39  (1902),  Starnes,40 
Alwood  and  Price,41  Card  and  Sprague42  (1903),  Clinton,44  Sheldon45 
(1905),  Heald46  (1906),  Scott,47  Faurot,48  Stone  and  Monahan,49 
Kern50   (1907),  Dandeno,51  Reade,52  Blake53   (1908),  Pollock,54  Scott 


16  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION 

and  Ayers55  (1909),  Lewis,56  Pollock,57  Scott  and  Ayers,58  Stewart,59 
Scott  and  Quaintance60  (1910),  Scott  and  Quaintance61  (1911), 
Demaree,62  Whetzel63  (1912),  Cook,04  Jehle,65  Matheny66  (1913), 
Conel,68  Cooley,69  Orton,70  Jehle71  (1914),  Bailey,72  Jackson,73  Posey,74 
Stakman  and  Rose,75  Heald,76  Valleau,77  Hawkins78  (1915),  Bartram,79 
Brooks  and  Cooley,80  Brooks  and  Fisher,81  Hessler82  (1916),  Pollock84 
(1918),  Willaman,92  Home,87  Willaman,93  Howard,89  McCubbin,86 
Cook,90  Anderson,94  Cook91  (1920),  Roberts,95  Ezekiel,96  Howard  and 
Home97  (1921),  Barss,98  Ezekiel,99  Brooks  and  Fisher,100  Norton, 
Ezekiel  and  Jehle101  (1923),  Norton, and  Ezekiel,102  Brooks  and 
Fisher103  (1924). 

In  1902  Norton37  discovered  the  apothecial  stage  of  the  brown  rot 
fungus  in  this  country  and  named  it  Sclerotinia  fructigena  because 
the  imperfect  stage  occurring  here  was  then  commonly  regarded  as 
Monilia  fructigena.  Subsequent  studies  of  this  form  by  other  investi- 
gators led  to  the  general  opinion  that  what  Norton  really  found  was 
the  perfect  form  of  S.  cinerea  and  not  S.  fructigena  as  he  supposed. 
Also  it  was  concluded  that  S.  fructigena  never  has  occurred  in  this 
country  and  that  the  fungus  occurring  here  should  never  have  been 
called  by  any  other  name  than  S.  cinerea.  Accordingly  the  great 
majority  of  writers  have  referred  to  the  American  brown  rot  fungus 
as  Sclerotinia  cinerea  until  as  late  as  1920. 

In  1920  Wormald88  demonstrated  that  while  S.  cinerea  of  Europe 
and  America  are  practically  identical  morphologically,  biologically 
they  may  be  distinguished  with  comparative  ease  and  suggested  the 
new  name  S.  cinerea,  forma  americana  for  our  brown  rot  fungus. 

In  1923  Norton  and  Ezekiel102  presented  a  paper  before  the 
American  Phytopathological  Society  at  Cincinnati  confirming  Wor- 
mald's  work.  A  brief  abstract  of  their  paper  appeared  in  Phyto- 
pathology in  1924  suggesting  that  the  American  brown  rot  fungus  be 
renamed  Sclerotinia  americana  Wormald,  since  in  their  opinion  it  can 
no  longer  be  considered  identical  with  8.  cinerea  of  Europe.  Whether 
this  very  recent  reclassification  will  meet  with  the  general  approval 
of  other  investigators  will  depend  largely  to  what  extent  Wormald 's 
work  has  been  confirmed  by  Norton  and  Ezekiel  whose  publication 
giving  the  details  of  their  work  has  not  yet  appeared. 

Posey74  and  Barss98  believe  there  are  two  distinct  forms  of  the 
brown  rot  fungus  in  Oregon,  and  in  recent  years  Wormald85  has  shown 
that  even  the  two  accepted  species  of  the  brown  rot  fungus  in  Europe 
have  each  at  least  two  distinct  biologic  strains. 


Bulletin  383]  BROWN  ROT  OF  APRICOTS  17 

Other  forms  of  the  brown  rot  fungus  have  been  described,  possibly 
the  best  known  of  which  is  Sclerotinia  laxa  (Ehrenb.)  Ader.  and 
Ruhl.  Many  investigators,  however,  insist  it  is  identical  with  S. 
cinerea. 

Possibly  the  first  published  account  of  the  disease  in  California, 
that  of  Professor  F.  T.  Bioletti36  of  the  University  of  California, 
appeared  in  the  Pacific  Rural  Press  following  a  severe  outbreak  of  the 
disease  in  ripening  Moorpark  apricots  at  Niles.  He  briefly  discussed 
the  cause  of  the  disease  saying,  "It  is  particularly  injurious  to  peaches 
in  the  eastern  states  and  to  prunes  and  apricots  on  the  Pacific  slope. ' ' 
He  was  fully  aware  that  the  disease  also  attacks  the  blossoms  and 
young  growth  of  the  peach  and  concluded  that  "the  same  probably 
occurs  in  the  case  of  apricots  and  other  fruits. '  "* 

Since  1902  frequent  references  to  brown  rot  may  be  found  in  the 
Annual  Report  of  the  California  Agricultural  Experiment  Station. 

In  1916  the  California  Agricultural  Experiment  Station  undertook 
experimental  spraying  for  the  control  of  the  disease.  No  conclusions 
were  drawn  because  climatic  conditions  prevented  an  attack.  In  1918 
Circular  204  appeared  with  recommendation  for  the  control  of  the 
disease,  but  investigational  work  was  not  resumed  until  1920.  In 
the  meantime  the  annual  loss  in  the  San  Francisco  Bay  region  due  to 
the  killing  of  the  blossoms  had  reached  alarming  proportions.  Orig- 
inally observed  as  a  disease  of  ripening  fruit,  the  apricot  industry  in 
the  coastal  regions  was  now  menaced  by  the  blossom  blight.  Because 
of  the  thoroughness  and  the  rapidity  with  which  the  blossoms  are 
destroyed  after  damp  cold  spells,  much  of  the  earlier  Monilia  blossom 
blight  damage  was  mistaken  for  frost  injury.  For  similar  reasons 
many  growers  attributed  the  disease  to  sour  sap,  sour  soil  and  other 
causes. 

The  results  of  the  first  year's  experiments  at  the  Deciduous  Fruit 
Station  are  contained  in  Bulletin  326,  and  the  present  paper  covers 
the  experimental  control  work  up  to  the  present  time. 


*  In  a  recent  personal  interview  Professor  Bioletti  stated  that  while  he 
had  never  seen  specimens  of  diseased  apricot  blossoms  when  he  wrote  his 
paper,  it  was  common  hearsay  at  the  time  that  they  were  attacked. 


18  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION 


IMPOETANCE  OF  THE  DISEASE  IN  CALIFOENIA 

No  accurate  estimate  of  the  annual  loss  occasioned  in  California 
by  Monilia  blossom  blight  can  be  given.  Unquestionably  the  loss  in 
fruit  alone,  to  say  nothing  of  the  great  cost  of  fighting  the  disease, 
has  amounted  to  hundreds  of  thousands  of  dollars  annually  in  the  past. 

Several  typical  examples  of  the  destructiveness  of  the  disease  may 
be  given :  In  one  orchard  in  the  Santa  Clara  Valley  the  disease  was 
so  bad  in  1920  that  only  $750  was  realized  from  about  nine  acres  of 
large  Blenheim  apricot  trees,  of  which  $250  was  paid  to  pick  the  occa- 
sional scattered  fruits.  Apricots  that  year  brought  $100  a  ton. 
Experienced  fruit  buyers  estimated  that  at  the  prevailing  price  the 
orchard  should  have  produced  $12,000  worth  of  fruit.  In  1921  at 
Berryessa  in  one  nine-acre  orchard  of  large  Blenheim  apricot  trees 
only  one  ton  of  fruit  was  picked.  Before  Monilia  blossom  blight  had 
invaded  this  orchard  it  regularly  produced  upwards  of  ninety  tons 
a  year. 

Many  fine  old  apricot  orchards  have  been  dug  up  in  the  past  five 
years,  others  have  been  virtually  abandoned,  and  many  hundred  acres 
of  trees  have  been  worked  over  to  more  resistant  varieties  of  prunes. 

In  addition  to  the  very  great  losses  occasioned  by  the  killing  of 
the  blossoms,  large  losses  have  been  sustained  by  the  rotting  of  the 
ripe  fruit.  Discussion  of  this  phase  of  the  disease  is  reserved  for  a. 
future  paper. 


Possible  Reasons  for  the  Increase  of  the  Disease  in  California 

Several  possible  reasons  for  the  increase  of  the  blossom  blight  phase 
of  the  disease  in  comparatively  recent  years  may  be  advanced :  It  may 
be  due  to  a  change  of  climate.  This  is  probably  the  least  tenable  of 
all  hypotheses.  But,  if  for  any  reason  the  coastal  regions  are  damper 
or  more  foggy  today  than  they  were  twenty  years  ago,  the  increase 
in  the  amount  of  the  disease  may  be  explained  on  this  basis. 

A  second  possible  reason  for  the  increase  of  the  disease  may  be 
found  in  the  fact  that  great  stretches  of  land  which  once  grew  hay  and 
grain  are  now  solidly  planted  with  apricots,  thus  facilitating  the  spread 
of  the  disease. 

Possibly  the  most  plausible  reason  for  the  increase  lies  in  the  fact 
that  varieties  more  susceptible  to  the  disease  are  now  being  grown. 


Bulletin  383]  BROWN  ROT  OF  APRICOTS  19 

Comparatively  a  few  years  ago  the  Moorpark  was  widely  cultivated. 
Today  it  is  virtually  a  thing  of  the  past.  It  is  an  excellent  eating  and 
drying  apricot,  but  it  bears  irregularly,  tends  to  ripen  unevenly,  also 
its  flat-sidedness  detracts  from  its  appearance  when  canned,  and  it 
"cooks  up"  making  a  cloudy  syrup.  It  is  therefore  unsuited  to  can- 
ning purposes  and  has  little  demand.  The  Blenheim  apricot,  par- 
ticularly adapted  to  coastal  conditions,  conforms  more  closely  to  can- 
ning requirements.  It  bears  heavily  and  regularly,  ripens  evenly,  also 
it  is  round  and  firm  and  does  not  produce  a  cloudy  syrup  when  canned. 
The  Moorpark  is  the  most  resistant  and  the  Blenheim  the  most  suscept- 
ible of  all  varieties.  Similarly  the  Hemskirk,  resembling  the  Moor- 
park in  many  ways  is  no  longer  planted  to  any  extent.  Other  varieties, 
better  adapted  to  the  climate  of  the  interior  valleys,  such  as  the  Tilton 
are  more  resistant  than  the  Blenheim,  but  under  certain  conditions 
they  may  suffer  severely  from  the  disease  as  is  true  of  even  the 
Hemskirk  and  Moorpark. 

Still  another  possible  reason  for  the  increase  of  the  disease  may  be 
that  the  fungus  has  become  better  adapted  to  the  attack  of  the  blossoms, 
or  a  new  strain  of  the  organism  may  have  been  introduced  into  the 
state.  Posey74  and  Barss98  claim  to  have  found  a  new  species  in 
Oregon. 


EXPERIMENTS  FOR  THE  CONTROL  OF  MONILIA  BLOSSOM 

BLIGHT 

INTEODUCTOEY  STATEMENT 

Since  1921  extensive  experiments  for  the  control  of  the  disease 
and  observations  of  the  results  obtained  by  private  orchards  with 
sprays  have  been  made. 

Scope  of  the  Experiments. — The  experiments  involved  the  use  of 
most  of  the  better  known  liquid  fungicides  as  well  as  oil  emulsions, 
miscible  oils,  coal-tar  derivative  sprays,  fungicidal  dusts  and  a  number 
of  proprietary  spray  materials  presumably  of  a  fungicidal  nature. 
About  one  hundred  distinct  treatments  were  tried,  involving  the  use 
of  these  materials,  separately  or  in  combination,  singly  or  in  multiple 
applications. 

The  value  of  orchard  sanitation  as  a  means  of  fighting  the  disease 
was  investigated. 


20  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  experiments  were  made  in  Santa  Clara,  Alameda,  San  Benito, 
Monterey  and  Santa  Cruz  counties.  Duplicate  experiments  were  also 
conducted  by  the  farm  advisors  in  most  of  these  counties  to  verify  the 
results  obtained  in  the  main  experiments. 

Orchards  used  in  the  experiments  were  of  the  Blenheim  variety,  old 
or  fully  mature,  of  uniform  size  and  in  a  very  seriously  diseased 
condition. 

The  Time  the  Sprays  were  Applied. — The  sprays  were  applied 
when  the  trees  were  fully  dormant  in  winter,  in  the  spring  when  the 
buds  were  swelling,  when  the  trees  were  coming  into  bloom,  and  when 
the  petals  had  fallen. 

The  Number  of  Trees  Used  in  the  Experiments. — Ten  to  thirty 
trees  were  included  in  each  sprayed  plot,  except  in  several  instances 
where  fewer  than  ten  trees  were  used.  The  actual  number  of  trees 
used  in  each  experiment  is  given  in  the  tables.  Check  plots,  usually 
consisting  of  ten  trees  each  were  left  at  suitable  points  in  the  orchards 
by  comparison  with  which  the  relative  degree  control  afforded  by 
any  treatment  was  determined. 

How  the  Sprays  were  Applied. — Bean  spray  pumps  and  spray  guns 
were  used  to  apply  the  different  sprays  at  a  pressure  of  200-300 
pounds.  The  tanks  were  carefully  cleansed  after  each  treatment.  Care 
was  taken  to  cover  all  parts  of  the  trees  with  as  little  waste  as  possible. 

Method  of  Determining  Results. — After  the  disease  had  run  its 
course  four  men  provided  with  hand  tally-counting  machines  counted 
the  infections  that  had  developed  in  the  sprayed  trees  and  check  trees. 
At  least  two  counts  were  made  from  each  tree  by  different  men,  and  if 
the  figures  varied  too  greatly  recounting  was  resorted  to  indefinitely 
until  a  satisfactory  count  was  obtained.  In  general  the  counts  ran 
very  close  together  even  in  trees  having  several  hundred  or  more 
infections.  A  difference  of  twenty  in  the  count  obtained  in  any  tree 
having  upward  of  two  hundred  infections  was  considered  too  great  and 
a  recount  made.  The  counts  taken  on  trees  having  little  disease  were 
usually  identical  or  very  nearly  so.  Only  freshly  killed  spurs,  one 
or  more  inches  in  length,  were  counted  unless  unmistakably  specimens 
of  Monilia  blossom  blight. 

The  average  number  of  infections  per  tree  was  obtained  by  dividing 
the  total  number  of  infections  counted  in  the  plot  by  the  number  of 
trees  in  the  j>lot.  This  method  determined  the  degree  of  relative 
control  afforded  by  the  treatment.  The  degree  of  practical  control 
;iikI  the  ultimate  success  of  any  treatment  was  determined  by  observing 


Bulletin  383]  BROWN  ROT  OF  APRICOTS  21 

how  closely  the  average  number  of  infections  per  tree  approximated 
a  certain  figure  considered  arbitrarily  as  the  point  of  failure.  Also 
the  general  effect  of  the  treatment  on  the  health  of  the  trees.  For 
instance,  the  degree  of  control,  relatively  speaking  might  be  very  great, 
but  from  the  practical  standpoint  very  poor.  Too  many  infections 
may  develop  in  a  tree  in  spite  of  a  spray  to  permit  of  even  a  fair-sized 
crop,  yet  when  compared  with  unsprayed  trees  the  control  has  been 
great.  Generally  speaking,  any  mature  apricot  tree  of  average  size 
having  one  hundred  killed  fruit  spurs  is  seriously  diseased  from  the 
practical  standpoint,  and  this  figure  was  used  as  a  basis  to  determine 
the  efficacy  of  the  spray  treatments.  Such  a  tree  presents  a  sorry 
sight,  and  an  orchard  which  will  average  one  hundred  infections  per 
tree  not  only  fails  to  produce  a  satisfactory  yield,  but  its  value  is 
greatly  depreciated. 

Similarly,  no  treatment  was  considered  successful  which  injured 
the  trees,  regardless  of  whether  the  control  was  good  or  bad.  Fungi- 
cides containing  sulfur  were  regarded  as  failures,  therefore,  as  this 
element  proved  harmful  to  apricot  trees. 

Observations  Made  in  Private  Orchards. — Counts  were  made  of  the 
infections  in  approximately  two  hundred  private  orchards  in  Napa, 
Santa  Clara,  San  Benito  and  Monterey  counties  in  the  past  four  years. 
In  no  instance  were  counts  made  unless  the  owner  could  give  accurate 
data  of  the  exact  strength  of  spray  materials  used  and  when  they  were 
applied.  A  number  of  these  orchards  were  sprayed  under  the  direct 
supervision  of  the  University,  which  in  some  instances  also  furnished 
the  materials  used.  The  use  of  brackets  throughout  the  tables  of  this 
paper  indicates  that  the  blocks  examined  adjoined  each  other  and 
were  of  the  same  size,  age  and  variety. 

The  Explanation  of  Terms. — The  following  explanation  of  terms 
is  given  to  facilitate  reading  the  experimental  data. 

Bordeaux  Mixture. — The  well-known  fungicide  made  of  copper 
sulfate  (Bluestone)  and  unslaked  lime.  Figures  are  generally  placed 
after  the  name  of  the  spray  to  indicate  the  strength  of  the  mixture; 
the  first  figure  indicates  the  number  of  pounds  of  bluestone  used,  the 
second  the  number  of  pounds  of  lime  and  the  last  the  number  of  gal- 
lons of  water.  Bordeaux  4-4-50  is  known  as  "standard  strength," 
Bordeaux  5-5-50,  "winter  strength"  and  Bordeaux  8-8-50  "double 
standard  strength." 

Fungicidal  Dusts. — Powders  or  dusts  having  fungicidal  prop- 
erties, blown  directly  upon  the  trees  with  a  bellows  or  power  blower. 


22  UNIVPJRSITY   OF   CALIFORNIA EXPERIMENT   STATION 

These  materials  are  usually  composed  largely  of  some  inactive,  harm- 
less substance  known  as  a  "filler"  or  "carrier"  which  carries  the 
fungicide  with  which  it  is  mixed  to  the  trees.  Fillers  commonly  used 
are  air-slaked  lime,  kaolin,  talc  and  sublimed  sulfur. 

Lime-Sulfur  Solution  1-10  (Winter  Strength). — Ordinary  com- 
mercial lime-sulfur  solution,  32°-34°  Baume,  used  at  the  rate  of  one 
gallon  of  the  solution  to  nine  gallons  of  water. 

Self-Boiled  Lime-Sulfur  8-8-50  (Standard  Strength). — In  this 
mixture  the  8  pounds  of  superfine  sulfur  is  partially  cooked  by  the 
heat  generated  when  the  8  ponds  of  unslaked  lime  is  allowed  to  slake 
in  part  of  the  water.  At  the  end  of  5  minutes  of  boiling,  the  mixture 
is  quickly  cooled  by  the  addition  of  the  rest  of  the  water. 

Orchard  Sanitation. — Here  used,  the  term  refers  to  removing 
and  destroying  all  twigs,  fruit  spurs  and  mummied  fruits  which  have 
been  killed  by  the  fungus  and  which  might  serve  as  a  source  of 
reinfection. 

Dormant  Spray. — One  applied  when  the  trees  are  wholly  inactive 
or  dormant  in  winter. 

Delayed  Dormant  Spray. — One  applied  very  early  in  the  spring 
when  the  buds  are  swelling  but  before  the  red  bud  appears  in  the  case 
of  the  apricot. 

Red  Bud  Spray. — One  applied  after  the  full  red  bud  has  appeared 
but  before  the  flowers  are  open. 

Pre-Bloom  Spray. — Any  spray  applied  before  the  flowers  open. 
The  dormant,  delayed  dormant  and  red  bud  sprays  are  pre-bloom 
sprays. 

Bloom  Sprays. — Sprays  applied  as  the  trees  are  coming  into  bloom. 
A  ' '  half -bloom  spray ' '  is  one  applied  when  half  the  flowers  are  open. 
A  ' '  full  bloom  spray ' '  is  one  applied  when  the  trees  are  in  full  bloom. 

Sprayed  in  the  Jacket. — Sprayed  after  the  bloom  has  passed,  but 
before  the  old  flower  parts  have  fallen  away. 

Multiple  Spraying. — The  use  of  more  than  one  application  of 
spray  to  control  fungus  and  insect  pests. 

Check  Trees  ;  Check  Plot. — Untreated  trees  or  plots  of  trees  by 
comparison  with  which  the  degree  of  control  afforded  by  any  treat- 
ment applied  under  identical  conditions  may  be  determined. 


Bulletin  383] 


BROWN    ROT    OF   APRICOTS 


23 


DOEMANT  SPEAYS 

Experimental. — Dormant  sprays  were  tested  in  1921  in  the  John 
Fahey  orchard  at  Sunnyvale  which  consists  of  Blenheim  apricots, 
25  years  of  age,  of  very  uniform  size  and  pruned  in  the  usual  way. 
The  sprays  used  were  Bordeaux  5-5-50  and  Lime-Sulfur  solution  1-10. 

TABLE  1 

Eesults  Obtained  with  Dormant  Sprats  in  the  John  Fahey  Orchard  in  1921 


Material  used 

Number  of 

trees  in 

plot 

Maximum 

number  of 

infections 

per  tree 

Average 
number  of 
infections 

per  tree 

Per  cent  of 
disease  com- 
pared with 
check  plot 

Bordeaux  5—5—50 

10 
10 
10 

205 
414 
245 

102 
296 
184 

34.4 

Check  plot 

Lime-sulfur  solution  1-10 

62.1 

The  table  shows  that  while  only  34.4  per  cent  as  many  infections 
developed  in  the  plot  sprayed  with  Bordeaux  as  in  the  unsprayed  plot 
adjoining,  the  actual  number  of  infections  exceeded  the  number 
regarded  arbitrarily  as  indicative  of  failure  from  the  practical  stand- 
point. The  control  with  lime-sulfur  was  even  poorer.  Both  treatments 
were  regarded  as  failures  from  the  practical  standpoint. 

A  similar  experiment  was  made  in  1922  in  the  22-year-old  Blenheim 
apricot  orchard  at  Berryessa  belonging  to  Mrs.  G.  Vennum  with 
similar  results. 

Results  Obtained  in  Private  Orchards  with  Dormant  Sprays. — In 
private  orchards  fungicidal  sprays  are  rarely  used  during  the  dormant 
period,  but  a  few  orchards  were  visited  which  had  been  sprayed  with 
fungicides  at  winter  strength  during  the  dormant  period.  In  these 
the  average  number  of  infections  per  tree  was  invariably  high,  and  the 
degree  of  control  a  failure  from  the  practical  standpoint. 


DELAYED  DOEMANT  AND  EED  BUD  SPEAYS 

Successful  Results  Obtained  in  Private  Orchards. — In  the  work  of 
Howard  and  Home97  the  only  control  obtained  was  with  delayed 
dormant  or  red  bud  sprays,  either  of  which  proved  equally  efficacious. 
Observations  made  in  private  orchards  during  the  past  four  years 
largely  confirm  their  work.    See  Table  2. 

The  following  tables  show  a  degree  of  control  that  was  highly  satis- 
factory from  either  the  relative  or  the  practical  standpoint. 


24 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Unsuccessful  Results  Obtained  in  Private  Orchards* — While  a 
spray  applied  just  before  the  blossoms  open  is  the  best,  such  a  spray 
is  not  always  successful.  In  badly  infected  orchards  situated  in 
regions  normally  damp  during  the  blossoming  period,  either  the 
delayed  dormant  or  the  red  bud  spray  may  fail  to  give  the  practical 
control  sought  for.    See  Table  3. 


TABLE  2 

Results  Obtained  with  Delayed  Dormant  or  Red  Bud  Sprays  in 

Private  Orchards 


Orchardist 

Locality 
and  year 

Treatment 

Number  of  sprayed 

trees. 

Age  of  trees,  variety. 

Average  number  of 

infections. 

Number  of  unsprayed 

trees. 

Age  of  trees,  variety. 

Average  number  of 

infections. 

I.  Higgins , 

Mt.  View 

Bordeaux  5-6-50. 

46  trees  examined. 

4  trees  examined. 

1922 

Delayed  Dormant. 

15-year  Blenheims. 
9  infections,  average. 

15-year  Blenheims. 
94  infections,  average. 

Higgins 

Mt.  View, 
1922 

Bordeaux  5-6-50. 
Delayed  Dormant. 

51  trees  examined. 
15-year  Blenheims. 

7  infections,  average. 

Malovina 

Unsprayed. 

52  trees  examined. 

15-year  Blenheims. 

178  infections,  average. 

Churin 

Mt.  View, 
1922 

Bordeaux  5-6-50. 
Red  Bud  spray. 

34  trees  examined. 
30-year  Blenheims. 

11  infections,  average. 

Popovitch 

Unsprayed. 

38  trees  examined. 

30-year  Blenheims. 

184  infections,  average. 

G.  H.  Bacon 

Hollister, 

Bordeaux  5-5-50. 

12  trees  examined. 

12  trees  examined. 

1923 

Red  Bud  cracking. 

20-year  Blenheims. 
7  infections,  average. 

20-year  Blenheims. 
104  infections,  average. 

Corotto 

Hollister, 
1923 

Bordeaux  8-8-50. 
Red  Bud  spray. 

12  trees  examined. 
10-year  Blenheims. 

15  infections,  average. 

Picetti 

Unsprayed. 

12  trees  examined. 

10-year  Blenheims. 

127  infections,  average. 

Although  the  treatments  caused  a  large  dimunition  of  infection,  it 
was  insufficient  to  have  any  practical  value. 

Results  Obtained  Experimentally  with  Red  Bud  Sprays. — Red  bud 
sprays  were  tested  in  the  John  Fahey  orchard  in  1921.  Mr.  Fahey 
had  just  purchased  the  orchard  which  had  received  no  sanitary  prun- 


*  The  badly  infected  condition  of  these  orchards  at  the  time  of  spraying 
was  due  to  the  fact  that  the  vital  importance  of  cleaning  up  the  trees  was 
then  little  appreciated.  Most  of  the  orchards  had  been  pruned  in  the  customary 
manner,  which  is  often  insufficient  for  the  ultimate  control  of  the  disease. 


Bulletin  383] 


BROWN    ROT    OF    APRICOTS 


25 


TABLE  3 

Unsuccessful  Results  Obtained  with  Sprays  Applied  just  Before  the 
Opening  of  the  Blossoms  in  Private  Orchards 


Orchardist 

Locality 
and  year 

Treatment 

Number  of  sprayed 

trees. 

Age  of  trees. 

Average  number  of 

infections. 

Number  of  unsprayed 

trees. 

Age  of  trees. 

Average  number  of 

infections. 

Holmes 

Berry  essa, 
1921 

Lime-sulfur 
solution  1-10. 

43  trees  examined. 
25  years  old. 

35  trees  examined. 

25  years  old. 

Red  Bud  spray. 

246  infections,  average. 

311  infections,  average. 

Bache 

Campbell, 
1921 

Bordeaux  4-5-50. 
Red  Bud  spray. 

42  trees  examined. 
30  years  old. 

4  trees  examined. 

30  years  old. 

200  infections,  average. 

536  infections,  average. 

Vennum 

Berry  essa, 
1921 

Bordeaux  4-5-50. 
Red  Bud  spray. 

36  trees  examined. 
22  years  old. 

35  trees  examined. 

22  years  old. 

168  infections,  average. 

180  infections,  average. 

Flickinger 

Berry  essa, 

Bordeaux  4-4-50. 

49  trees  examined. 

49  trees  examined. 

1921 

Red  Bud  spray. 

20  years  old. 
121infections,  average. 

20  years  old. 
135  infections,  average. 

Jensen* 

Hollister, 
1922 

Bordeaux  5-5-50. 
Red  Bud  cracking. 

6  trees  examined. 
25  years  old. 

223  infections,  average. 

"Buggo"   Crude  Oil 

6  trees  examined. 

Emulsion  30-200. 

25  years  old. 

Red  Bud  cracking. 

373  infections,  average. 

Check  plot. 

6  trees  examined. 
25  years  old. 
473  infections,  average. 

Dry  Lime-sulfur 

6  trees  examined. 

10-40. 

25  years  old. 

Red  Bud  cracking. 

401  infections,  average. 

Bordeaux  5-5-50. 

6  trees  examined. 

Red  Bud  cracking 

25  years  old. 

(duplicate). 

281  infections,  average. 

King 

Hollister, 

Bordeaux  6-6-50. 

9  trees  examined. 

1923 

Red  Bud  spray. 

11  years  old. 
348  infections. 

Lewis 

Unsprayed. 

9  trees  examined. 

10  years  old. 

1,723  infections, 
average. 

Renzf 

Hollister, 

Bordeaux  7-8-50. 

10  trees  examined. 

1923 

Red  Bud  spray. 

17  years  old. 
123  infections. 

Hamilton 

Unsprayed. 

10  trees  examined. 

30  years  old. 

1,001  infections, 

average. 

*  Figures   compiled  from   demonstration   plots   of   Mr.    W.   J.  Tocher,   Farm   Advisor,    San 
Benito  County. 

t  Renz's  trees  though  younger  than  Hamiltons  were  equally  large. 


26  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

ing,  and  it  contained  therefore  much  infective  material.  Damp  weather 
prevailed  at  times  during  the  blossoming  period.  In  those  parts  of 
the  orchard  where  the  disease  had  been  the  worst,  Bordeaux  gave  the 
best  results.    See  Table  4. 

These  results  were  of  no  practical  value.  In  all  cases  the  infections 
were  greatly  in  excess  of  the  number  regarded  as  indicative  of  failure. 
This  failure  was  in  part  due  to  the  condition  of  the  trees. 


TABLE  4 

Results  Obtained  with  Single  Eed  Bud  Sprays  in  the 

Orchard  in  1921 

:  John  Fahey 

Spray  materials  used 

Number  of  trees 
examined 

Average  number  of 
infections 

Bordeaux  4-5-50  plus  Dormant  Soluble  Oil  (a  miscible 
oil)  5-200 

27 
11 
21 

283 

Bordeaux  4—5—50 

264 

Bordeaux  4—5—50  (duplicate) 

229 

The  Most  Favorable  Period  for  Securing  Good  Results  with  One 
Spray. — The  best  results  with  single  sprays  are  obtained  at  the  delayed 
dormant  or  the  red  bud  stage,  and  the  nearer  the  buds  are  to  breaking 
and  to  showing  the  folded  white  petals  beneath  the  red  sepals,  the 
better  the  control. 

In  1921  Mr.  Chappel  near  Sunnyvale  sprayed  his  orchard  in  the 
red  bud  stage  with  Bordeaux  30-30-200.  In  a  block  of  42  trees  on  a 
strip  of  gravelly  soil  where  most  of  the  buds  showed  the  white  of  the 
petals,  the  average  number  of  infections  was  18  to  the  tree.  In  a 
near-by  block  of  122  trees  on  a  heavier  soil,  where  the  buds  were  much 
less  advanced,  the  average  number  of  infections  was  103.  The  develop- 
ment of  the  buds  is  earlier  in  light,  gravelly  soils  than  on  heavy,  clay 
soils. 

Later  Mr.  Chappel  sprayed  a  neighboring  orchard  belonging  to 
Mr.  McDaniel.  The  soil  here  was  also  heavy,  but  the  buds  somewhat 
more  advanced.  In  a  block  of  84  trees  the  average  number  of  infections 
was  43. 

The  general  orchard  conditions  in  the  three  cases  were  the  same. 
The  degree  of  control  therefore  was  in  proportion  to  the  nearness  of 
the  buds  to  the  point  of  breaking. 

Similar  instances  have  been  observed  repeatedly. 


Bulletin  383] 


BROWN    ROT    OF   APRICOTS 


27 


Fig.  8. — The  best  control  of  Monilia  blossom  blight  of  apricots  obtainable 
with  any  one  spray  is  secured  at  the  time  when  the  buds  are  cracking,  showing 
the  folded  white  petals  beneath  the  red  sepals,  as  shown  here  in  the  center  twig. 


28 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


BLOOM  SPEAYS 

Experimental. — Extensive  experiments  were  made  at  Hayward  in 
1923  and  at  Hollister  in  1924  with  sprays  applied  at  various  times 
during  the  bloom.  In  both  years  extremely  dry  weather  prevailed  in 
both  districts  and  no  conclusions  could  be  drawn,  as  the  disease  did  not 
appear. 

Results  Obtained  with  Full  Bloom  Sprays  in  Private  Orchards. — 
Observations  made  in  private  orchards  during  the  past  four  years  show 
that  sprays  applied  during  the  full  bloom  have  little  practical  value, 
although  at  times  the  decrease  of  infections  may  be  great,  just  as  in 
the  case  of  pre-bloom  sprays. 

TABLE  5 
Typical  Eesults  Obtained  in  Private  Orchards  with  Full  Bloom  Sprays 


Orchardist 

Locality 
and  year 

Treatment 

Number  of  sprayed 

trees. 

Age  and  variety. 

Average  number  of 

infections. 

Number  of  unsprayed 

trees. 

Age  and  variety. 

Average  number  of 

infections. 

Butts* 

Campbell, 
1921 

Bordeaux  30-30-200. 

33  trees  examined. 
35-year  Hemskirks. 

2  trees  examined. 

Small  Hemskirks. 

129  infections,  average. 

487  infections,  average. 

Lester  * 

Campbell, 
1921 

Bordeaux  30-30-200. 

72  trees  examined. 
25-year  Blenheims. 

4  trees  examined. 

8-10-year  Blenheims. 

178  infections,  average. 

363  infections,  average 

A   DiFiori 

San  Jose, 
1921 

Bordeaux  25-25-200. 

42  trees  examined. 
Old  Blenheims. 

114  infections,  average. 

Huff 

Mt.  View, 
1922 

Bordeaux  4-4-50. 

20  trees  examined. 
15-year  Blenheims. 

18  trees  examined. 

15-year  Blenheims. 

257  infections,  average. 

351  infections,  average. 

Hitchings 

Aromas, 
1924 

Bordeaux  30-32-200. 

10  trees  examined. 
30-year  Blenheims. 

131  infections,  average. 

*  The  check  trees  in  the  Butts  and  Lester  orchards  were  distinctly  smaller  than  the  sprayed 
trees.  There  can  be  no  doubt,  therefore,  that  the  spray  helped  a  little  considering  the 
excessively  high  counts  in  the  smaller  trees. 


In  every  orchard  listed  above  the  trees  showed  an  excessive  number 
of  infections,  and  the  treatments  must  be  regarded  as  of  no  practical 
value. 

Spraying  Before  the  Full  Bloom;  Results  Obtained  in  Private 
Orchards. — Observations  show  that  sprays  applied  when  the  trees  are 
half  or  two-thirds  in  bloom  are  ordinarily  useless.    In  fact,  the  longer 


Bulletin  383] 


BROWN    ROT    OF    APRICOTS 


29 


Fig.  9. — Apricots  sprayed  in  full  bloom,  too  late  for  control  of  brown  rot. 


30 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION 


spraying  is  delayed  after  the  flowers  start  to  open,  the  greater  the 
failure  is  apt  to  be,  since  fogs,  dew  or  rain  wetting  the  open  blossoms 
facilitate  the  attack  of  the  fungus. 

TABLE  6 

Results  Obtained  in  Private  Orchards  with  Sprays  Applied  when  One-Half 
or  Two-Thirds  of  the  Blossoms  were  Open 


Orchardist 

Locality 
and  year 

Treatment 

Number  of  sprayed 

trees. 

Age  and  variety. 

Average  number  of 

infections. 

Number  of  unsprayed 

trees. 

Age  and  variety. 

Average  number  of 

infections. 

Cinciamilla 

San  Jose, 
1921 

Bordeaux  30-30-200. 
2  /  z  bloom. 

29  trees  examined. 
32-year  Blenheims. 

282  infections,  average. 

Lowry 

Centerville, 
1922 

Bordeaux  5-5-50. 
]/2  bloom. 

25  trees  examined. 
25-year  Blenheims. 

10  trees  examined. 

25-year  Blenheims. 

318  infections,  average. 

324  infections,  average. 

Love 

Aromas, 
1922 

Bordeaux  5-5-50. 
14,  bloom. 

45  trees  examined. 
8-year  Blenheims. 

14  trees  examined. 

8-year  Blenheims. 

128  infections,  average. 

267  infections,  average. 

Butts 

Campbell, 

Bordeaux  5-5-50. 

9  trees  examined. 

2  trees  examined.* 

1922 

J^  bloom. 

35-year  Hemskirks. 
158  infections,  average. 

35-year  Hemskirks. 
1,377  infections, 
average. 

Kelly 

Hollister, 

Bordeaux  8-8-50. 

12  trees  examined. 

12  trees  examined. 

1923 

}/2  bloom. 

12-year  Blenheims. 
96  infections,  average. 

12-year  Blenheims. 
281  infections,  average. 

Nicholson 

Aromas, 
1924 

Bordeaux  7-7-50. 
H  bloom. 

10  trees  examined. 
38-year  Early  Golden. 

5  trees  examined. 

38-year  Early  Golden. 

419  infections,  average. 

555  infections,  average. 

*  The  two  check  trees  in  this  orchard  were  not  pruned.  The  excessively  great  number  of 
infections  was  made  possible,  no  doubt,  by  the  presence  of  so  much  infectious  material  left 
behind  in  the  trees. 

Regardless  of  the  stage  of  the  bloom,  the  number  of  infections  was 
very  great,  and  no  practical  control  was  obtained. 


MULTIPLE  SPEAYING 

All  sprays  diminish  infection  regardless  of  the  time  of  their  appli- 
cation, the  best  results  being  obtained  just  before  the  flowers  open. 
The  use  of  repeated  or  multiple  sprays  throughout  the  susceptible 
period  is  discussed  here. 

Multiple  spraying  for  disease  and  insect  control  is  not  new  to 
California.  The  control  of  thrips,  red  spider,  codlin  moth,  pear  scab 
and  peach  blight  frequently  require  more  than  one  spray.  Apple 
growers  frequently  spray  as  many  as  eight  times  for  the  control  of 
codlin  moth  alone. 


Bulletin  383] 


BROWN   ROT   OF   APRICOTS 


31 


Multiple  Spraying  in  the  Pre-Bloom  Period. — Table  2  shows  that 
under  certain  conditions  one  spray  applied  just  before  the  blossoms 
open  may  control  the  disease.  It  is  of  interest  to  determine  whether 
several  sprays  applied  in  the  pre-bloom  period  can  be  relied  upon 
regularly  to  control  the  disease.     It  seems  improbable  because  the 


.  :^( 

if* 

"It 

*      A 

a 


mgmmmm^  ~'~r7~'  '*-' 


•A   •!■  .  /    0'.  <.%t> 


r-.    n    (1    ft) 


^ 


^ 


\  / 


4  * 


% 


d 


Fig.  10. — Photomicrograph  of  asci  and  ascopores  of  brown  rot  fungus 

(copied  from  Matheny). 

several  sprayings  are  confined  to  a  period  when  the  disease  is  unable 
or  little  likely  to  make  its  attack,  and  no  spray  reaches  the  delicate 
petals  or  reproductive  parts  of  the  flowers  later  to  be  exposed.  Even 
assuming  sprays  applied  in  the  pre-bloom  to  have  killed  all  the  spores 
in  the  trees,  there  is  nothing  to  prevent  fresh  spores  being  blown  in 
from  outside  sources  to  attack  the  flowers  as  they  open. 


32 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


In  1921  extensive  experiments  with  multiple  sprays  applied  in  the 
pre-bloom  were  made  in  the  John  Fahey  orchard  at  Sunnyvale. 


TABLE  7 

Eesults  Obtained  with  Multiple  Sprays  Applied  in  the  Pre-Bloom  Period  in 
the  John  Fahey  Orchard  at  Sunnyvale 


Treatment 

Number  of 

trees  in 

plot 

Average 
number  of 
infections 

per  tree 

Bordeaux  4—5—50.     Delayed  Dormant 

I            7 
1            8 
1            8 

r       io 
l        5 

f           5 
1            5 

r        5 

Bordeaux  4—5—50 .     Red  Bud 

207 

Lime-sulfur  solution  1—10.     Dormant 

Bordeaux  4—5—50.     Delayed  Dormant 

101 

Bordeaux  4-5-50.     Red  Bud 

Self-boiled  Lime-sulfur  8—8—50.     Delayed  Dormant 

Self-boiled  Lime-sulfur  8-8-50.     Red  Bud 

190 

Lime-sulphur  solution  1-10.     Dormant 

Self-boiled  Lime-sulfur  8—8—50.     Delayed  Dormant 

187 

Self-boiled  Lime-sulfur  8-8-50.     Red  Bud 

Bordeaux  5—5—50.     Dormant 

"Ortho"  crude  oil  emulsion  15-200  plus  lime-sulfur  solution  1-10.     Red 
Bud 

117 

Lime-sulfur  solution  1-10.     Dormant 

"Ortho"  crude  oil  emulsion  15-200  plus  lime-sulfur  solution  1-10.     Red 
Bud 

358 

Bordeaux  5—5—50.     Dormant 

Bordeaux  4-5-50  plus  "Dormant  Soluble  Oil"  5-200  (a  miscible  oil)  Red 
Bud 

165 

Lime-sulfur  solution  1—10.     Dormant 

Bordeaux  4-5-50  plus  "Dormant  Soluble  Oil"  5-200  (a  miscible  oil)  Red 
Bud 

217 

The  results  of  these  experiments  prove  that  in  unsanitary  orchards 
in  localities  normally  damp  during  the  blossoming  period  two  or  more 
sprays  applied  in  the  pre-bloom  period  may  fail  to  give  the  practical 
control  sought. 

Multiple  Spraying  Throughout  the  Susceptible  Period  of  the 
Blossoms. — Multiple  spraying  throughout  the  susceptible  period  was 
tested  in  1922  in  the  G.  Vennum  orchard  at  Berryessa,  in  the  H.  Owen 
orchard  at  Hayward  in  1923,  and  in  the  H.  Smith  orchard  at  Hollister 
in  1924.  No  definite  conclusions  were  drawn  because  the  disease  did 
not  appear  owing  to  an  almost  unprecedented  drought  during  the 
susceptible  period  in  the  last  two  regions  in  1923  and  1924,  and  because 
the  Vennum  orchard  failed  to  bloom  properly  in  1922.  Duplicate 
experiments  conducted  by  farm  advisors  in  other  localities  normally 
<l;irnp  those  years  furnished  much  valuable  data  as  did  observations 
made  in  private  orchards.    See  Table  8. 


Bulletin  383] 


BROWN    ROT    OF    APRICOTS 


33 


TABLE  8 
Results  Obtained  with  Multiple  Sprays  Applied  During  the  Susceptible 

Period  of  the  Blossoms 


Orchardist. 

Locality  and  year. 

Age  of  trees  and  variety. 


G.  Love.* 
Aromas,  1922. 
8-year  Blenheims. 

E.  Seeley.2 
Aromas,  1922. 
24-year  Blenheims. 

L.  Carroll.3 
Campbell,  1922. 
27-year  Blenheims. 


C.  L.  Chapman. 
Hollister,  1923. 
6-year  Blenheims. 

F.  P.  Gettings.« 
Hollister,  1923. 
13-year  Blenheims. 


B.  Jensen.5 
Hollister,  1923. 
29-year  Blenheims. 


Num- 
ber of 
trees 


14 
45 
56 

6 
6 

7 

2 
22 
14 
14 

12 

12 

6 
12 

11 

14 

12 

7 

7 

14 


Treatment 


Unsprayed 

Bordeaux  5-5-50. 
Bordeaux  5-5-50. 

Unsprayed 

Bordeaux  5-5-50. 
Bordeaux  5-5-50. 

Bordeaux  6-7-50. 
Bordeaux  6-7-50. 
Bordeaux  6-7-50. 
Bordeaux  6-7-50. 
falling 


3^  bloom 

l/5  and  XA  bloom. 


Red  Bud 

Red  Bud  and  Full  Bloom. 


Full  Bloom 

1%  bloom 

1%  and  90%  bloom 

1%;  90%  bloom  and  petals 


Bordeaux  73^-7^-50.     Red  Bud 

Bordeaux    7^-7^-50.     Red    Bud    and    Full 
Bloom 


Unsprayed 

Crude  oil  emulsion  30-200.     Dormant  Bordeaux 

8-8-50.     Red  Bud 

Crude  oil  emulsion  30-200.     Dormant  Bordeaux 

8-8-50.     Red  Bud  and  Y2  bloom 

Crude  oil  emulsion  30-200.     Dormant  Bordeaux 

8-8-50.     Red  Bud 

Crude  oil  emulsion  30-200.     Dormant  Bordeaux 

8-8-50.     Red  Bud  and  Y2  bloom 


Unsprayed 

Bordeaux  8-8-50. 
Bordeaux  8-8-50. 


Red  Bud 

Red  Bud  and  l/3  bloom. 


Average 
number  of 
infections 

per  tree 


267 
128 

48 

239 

85 
12 

102 
52 
30 

13 
85 

48 
256 

52 

29 

63 

11 

148 
61 
40 


1  Demonstration  plots  of  Mr.  T.  C.  Mayhew,  Farm  Advisor,  Monterey  County. 

2  Demonstration  plots  of  Mr.  T.  C.  Mayhew,  Farm  Advisor,  Monterey  County. 

3  These  different   blocks  while   not   immediately   adjoining  were   very   close   to   one  another 
in  the  same  orchard  and  subject  to  identical  conditions. 

4  The  block   of  unsprayed  trees   in   this    orchard   did   not   immediately   adjoin   the   sprayed 
plots  but  was  very  close  and  subject  to  identical  conditions. 

5  Demonstration  plots  of  Mr.  W.  J.  Tocher,  Farm  Advisor,  San  Benito  County. 

The  above  table  shows  a  control  of  the  disease  proportional  to  the 
number  of  sprays  applied  during  the  susceptible  period  of  the  blossoms. 

The  use  of  multiple  sprays  throughout  the  susceptible  period  of  the 
blossoms  starting  with  the  red  bud  spray,  which  is  absolutely  indis- 
pensible,  and  ending  with  the  full  bloom  or  even  a  little  later  when 
the  petals  have  been  shed  is  the  only  method  likely  to  secure  practical 
results  in  badly  infected  orchards  situated  in  localities  normally  damp 
during  the  blossoming  period.  The  method  is  logical  since  it  destroys 
the  greater  part  of  the  accumulation  of  spores  in  the  trees,  and  it 
insures  protection  to  all  parts  of  all  flowers  as  they  continue  to  be 
exposed. 


34  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


DISCUSSION 

Reasons  for  Failure  of  Single  Sprays  to  Control  the  Disease. — The 
possible  reasons  for  failure  of  single  sprays  applied  during  the  red 
bud  stage,  the  period  most  likely  to  secure  good  results,  are  many : 
careless  or  hurried  spraying,  weak  or  unsuitable  fungicides,  lack  of 
orchard  sanitation  and  other  factors  might  easily  lead  to  failure.  These 
factors  can  be  corrected. 

A  factor  that  cannot  be  corrected,  and  which  frequently  renders 
control  difficult  is  the  relatively  long  susceptible  period  of  the  blossoms. 
The  blossoming  period  may  last  for  weeks  with  favorable  temperature. 

The  disease  rarely  attacks  the  tight  red  buds  and  then  chiefly 
through  insect  wounds  and  abrasions.  Clusters  of  buds  may  die  as 
the  result  of  the  infection  of  the  spur  through  wounds  or  of  a  single 
infected  early  blossom,  but  this  is  not  a  direct  attack  on  the  unopened 
buds.  As  soon  as  the  petals  show,  however,  the  blossoms  may  be 
destroyed. 

A  spray  applied  just  before  the  red  buds  open  gives  the  best  results 
because  it  destroys  most  of  the  spores  that  have  been  produced  in  the 
trees.  Unfortunately  the  spray  does  not  kill  the  fungus  living  in  the 
dead  twigs  and  mummies  left  in  the  trees.  Many  other  investigators 
including  Bourcart67  who  quotes  the  observations  of  Prilleux  (p.  237) 
and  von  Tubeuf  (p.  259)  have  noted  this.  Also  if  moisture  conditions 
continue  favorable,  fresh  spores  will  be  produced  in  spite  of  the 
presence  of  the  fungicide.  Then  again,  the  pustules  are  very  dusty  or 
powdery  with  spores  which  causes  the  spray  to  be  shed  off  without 
wetting  them.  Also,  much  dead  wood  remains  untouched  even  in  well 
sprayed  trees,  and  upon  it  the  fungus  may  fruit  unhampered.  Lastly, 
a  spray  applied  to  the  red  buds,  only  directly  protects  the  red  sepals. 
These  curl  back  and  under  as  the  petals  and  reproductive  parts  are 
exposed.  The  latter  having  no  fungicide  upon  them  are  open  to  attack 
from  spores  blown  in  from  outside  sources  or  those  produced  in  the 
trees  themselves. 

Reasons  for  the  Failure  of  Dormant  Sprays  to  Control  the  Disease. 
Dormant  sprays  are  usually  very  ineffective,  not  only  for  the  reasons 
given,  but  because  much  of  the  spray  is  washed  off  before  the 
susceptible  arrives. 

Reasons  for  the  Failure  of  Full  Bloom  Sprays  to  Control  the 
Disease. — Such  sprays  ordinarily  fail  because  much  infection  has 
already  taken  place  before  the  sprays  are  applied.     If  by  any  chance 


Bulletin  383] 


BROWN    ROT    OF   APRICOTS 


35 


the  long  period  between  the  time  when  the  first  blossoms  show  and  the 
full  bloom  when  the  spray  is  applied  be  characterized  by  clear  days 
and  dry  nights  the  spores  will  not  germinate  and  there  will  be  no 
disease.  Such  an  almost  unprecedented  case  as  this  occurred  in  certain 
parts  of  Santa  Clara,  Alameda  and  San  Benito  counties  in  1923  and 
1924.  Under  such  conditions  the  disease  did  not  appear  even  in  those 
orchards  which  had  suffered  the  worst  in  other  years. 

Conditions  under  which  Red  Bud  Sprays  Succeed. — In  dry  locali- 
ties where  the  climatic  conditions  are  unfavorable  to  the  ready  produc- 
tion of  spores,  a  single  red  bud  spray  is  frequently  effective.  It  may 
be  sufficient  even  in  damp  localities  in  dry  seasons  or  in  any  season  if 
the  sources  of  infection  are  reduced  by  thoroughly  cleaning  up  of  the 
orchard. 

Reasons  for  the  Sioccess  of  the  Multiple  Spray  Treatment. — In 
localities  normally  very  damp  during  the  susceptible  period,  and  in 
badly  infected  orchards,  the  multiple  spray  method  gives  adequate 
protection  to  all  parts  of  all  flowers  as  they  open  day  after  day.  More- 
over, each  spray  destroys  spores  which  escaped  the  earlier  sprays,  and 
destroys  many  of  the  spores  produced  after  the  last  spraying. 


OECHAED  SANITATION 

The  Eelation  of  Careful  Pruning  to  Spraying  in  the  Control  of  the  Disease 

Experiments  have  shown  a  direct  relationship  between  the  control 
obtained  with  sprays  and  the  amount  of  infectious  material  left  in 
the  trees. 

In  1921  all  the  old  twigs  and  mummies  were  pruned  from  seven 

mature  Blenheim  apricot  trees  in  Mr.  Morgan's  orchard  at  Mountain 

View.     Trees  adjoining  were  pruned  in  the  ordinary  manner.     The 

trees  in  both  blocks  were  given  a  red  bud  spray  of  lime-sulfur  solution 

1-10.     All  other  conditions  were  equal.     The  results  are  shown  in 

Table  9. 

TABLE   9 


Kind  of  pruning 

Row  number 

Number  of  trees 

Average  number 

of  infections 

per  tree 

Pruned  carefully 

1  and  2 

r       3 

7 
4 
9 
9 

45 

Pruned  in  the  usual  way 

115 
135 

134 

About  three  times  as  much  disease  developed  in  the  trees  pruned 
in  the  ordinary  manner  as  in  those  pruned  with  care. 


36 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


In  1922,  similar  experiments  were  conducted  in  two  blocks  of 
6-year-old  Blenheim  trees  in  the  orchard  of  Mrs.  G.  Vennum  of  Berry  - 
essa.  The  trees  were  sprayed  with  Bordeaux  7V2_7%_50  when  the  red 
buds  were  cracking.    See  Table  10. 


TABLE  10 


Number  of  trees 

Carefully  pruned 
Average  number  of  infections 

Usual  pruning 
Average  number  of  infections 

Block  1: 

34 

15 
30 

37 

30 

Block  2: 

31 

140 

42 

Ordinary  Pruning  Better  than  No  Pruning 

Orchards  were  visited  in  which  some  of  the  sprayed  trees  were  not 
pruned.  Results  obtained  in  the  Freese  orchard  in  1921  are  typical 
for  such  treatment.     See  Table  11. 


TABLE  11 


Orchardist 

Locality  and  year 

Age  and  variety 

Number 

of  trees 

examined 

Treatment 

Pruned 
trees 

Unpruned 
trees 

A.  F.  Freese. 
Campbell,  1921. 

63 

35 

2 

Dry   Lime-sulfur     113^    lbs.-50    gals. 
Red  Bud  Spray 

206 

25-year  Blenheims. 

Dry   Lime-sulfur    113^    lbs.-50    gals. 
Red  Bud  Spray 

390 

Unsprayed  * 

707 

*  The  unsprayed   trees   did  not  immediately   adjoin   the    sprayed   plots   but 
were  located  in  the  same  orchard  close  by  and  subject  to  similar  conditions. 

Neither  of  the  treatments  was  sufficiently  effective.  The  figures 
show,  however,  that  in  badly  infected  orchards  in  seasons  favorable 
to  the  development  of  the  fungus,  ordinary  pruning  followed  by  a  red 
but  spray  may  not  be  sufficient  to  control  the  disease,  but  it  tends  to 
lessen  the  amount  of  infection. 

Under  certain  conditions  careful  pruning  may  equal  the  red  bud 
spray  in  the  control  of  the  disease.  At  Mountain  View  the  old  Blen- 
heim apricot  orchards  of  Messrs,  Morgan  and  Fagundes  adjoin.  The 
general  conditions  are  identical.  In  1922  Mr.  Morgan  pruned  his 
trees  in  the  usual  manner  and  sprayed  with  Bordeaux  5-5-50  in  the 
red  bud  stage.  Mr.  Fagundes  did  not  spray  but  pruned  his  trees  very 
carefully.    See  Table  12. 


Bulletin  383] 


BROWN   ROT    OF   APRICOTS 


37 


Growers  should  not  conclude  that  extra  careful  pruning  may  be 
consistently  substituted  for  spraying.  Both  are  vital  in  the  eventual 
control  of  the  disease.  Had  Mr.  Fagundes  sprayed  as  well  as  pruned 
in  the  manner  that  he  did,  a  much  lower  count  probably  would  have 
obtained  in  his  orchard. 

Wormald83  of  England,  discouraged  because  the  sprays  neither  kill 
the  fungus  within  the  wood  nor  even  prevent  its  fructification  on  the 
blighted  twigs  and  mummies,  and  because  liquid  fungicides  do  not 
adhere  to  the  spore  pustules  on  account  of  their  dusty  nature  states : 
"At  present  fruit  growers  are  strongly  advised  not  to  attempt  to 
control  this  disease  by  spraying  as  they  are  extremely  likely  to  waste 
their  time  and  money.  It  has  been  found  that  washes  generally  used 
for  checking  the  spread  of  the  disease,  for  instance,  lime  sulfur  and 
Bordeaux  mixture,  are  useless  as  they  fail  to  wet  the  pustules. ' ' 


TABLE  12 


Orchardist 

Number 
of  trees'"^ 
examined 

Sprayed  but  not  pruned 
Average  number  of  infections 

PrunedThnt  not  sprayed 
Average  number  of  infections 

Morgan 

16 
16 

62 

Fagundes 

60 

Sprays  may  not  adhere  to  the  spore  pustules,  but  they  do  adhere 
to  the  susceptible  flower  parts  and  to  a  large  degree  prevent  an  attack 
by  the  fungus.  And  sprays  probably  kill  large  numbers  of  spores 
lodged  in  various  parts  of  the  trees,  including  the  fringes  of  hair  on 
the  bud  scales,  which  eventually  might  find  their  way  to  the  susceptible 
flower  parts.  Sprays  have  been  too  successful  here  to  advise  discon- 
tinuing their  use.  But  in  wet  seasons  when  the  ground  is  too  boggy 
for  the  use  of  spray  rigs,  carefully  pruned  trees  unquestionably  will 
have  a  great  advantage  over  trees  pruned  in  the  ordinary  manner  or 
not  pruned  at  all. 

Theoretically  the  removal  of  all  blighted  twigs  and  mummies  from 
the  tree  should  render  unnecessary  the  use  of  sprays,  since  their 
removal  removes  the  fungus  itself.  Unfortunately  all  orchardists  are 
not  progressive  enough  to  do  this.  There  always  are  and  always  will 
be  neglected  orchards  to  serve  as  foci  for  the  dissemination  of  the 
disease.  That  the  disease  may  spread  from  orchard  to  orchard  is  evi- 
denced by  the  fact  that  in  sprayed  orchards  the  disease  is  invariably 
worse  near  seriously  diseased  unsprayed  trees.  The  great  preponder- 
ance of  reinfection,  however,  must  come  from  spores  produced  in  the 
trees  themselves,  since  in  sprayed  orchards  the  amount   of  disease 


38  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION 

decreases  very  suddenly  in  trees  a  comparatively  short  distance  away 
from  the  unsprayed  trees.  In  1922,  Mr.  Renz  of  Hollister  sprayed  with 
Bordeaux  7-8-50  in  the  red  bud  stage.  His  neighbor  did  not  spray. 
The  unsprayed  trees  averaged  1001  infections  each  in  a  block  of  ten 
trees.  In  the  same  number  of  trees  immediately  adjoining  in  the  Renz 
orchard,  the  average  number  of  infections  was  123.  Several  rows 
farther  away  from  the  unsprayed  trees  the  average  was  only  37,  and 
in  the  rest  of  the  orchard  the  count  was  low. 

The  Practicability  of  Careful  Pruning 

Many  growers,  skeptical  at  first  as  to  the  practicability  of  careful 
pruning,  now  admit  that  it  pays.  In  1922  Mr.  B.  Jenson  at  Hollister, 
pruned  his  orchard  in  the  ordinary  manner  and  sprayed  in  the  red 
bud  stage  with  Bordeaux  5-5-50.  In  two  blocks  of  trees  the  average 
number  of  infections  was  250  and  280.  The  following  year  the  orchard 
was  pruned  with  great  care  before  spraying.  The  counts  in  the  same 
blocks  averaged  61  and  65  each.  Even  his  unsprayed  trees  averaged 
only  148  infections  as  compared  with  473  in  1922.  And  1923  was 
very  favorable  to  the  disease  in  that  locality.  In  an  adjoining  orchard, 
unsprayed  and  unpruned,  the  average  number  of  infections  was  738. 
General  conditions  in  the  orchards  were  approximately  the  same. 

The  Disposal  of  Infectious  Material 

Prunings  should  be  raked  up  as  far  as  possible  and  burned.  The 
fungus  dies  out  in  them  the  second  year  after  infection.  Mummies 
may  continue  to  produce  spores  for  three  years.  Plowing  them  under 
destroys  most  of  them  and  renders  production  of  the  apothecial  form 
difficult  for  the  remainder. 

Experiments  to  Produce  the  Apothecial  Form 

The  apothecial  form  of  the  fungus  is  only  occasionally  found  in 
California,  conditions  apparently  not  being  generally  favorable  to  its 
development.  Approximately  one  thousand  apricot  mummies  were 
exposed  on  the  surface  or  partially  buried  in  the  ground  in  December, 
1921.  Before  spring  the  following  year  they  had  decomposed  leaving 
only  clean  seeds.    No  apothecia  had  developed  up  to  the  spring  of  1924. 

Ezekiel00  found  that  plum  mummies  chilled  for  a  time  would  pro- 
duce apothecia  within  twenty-live  weeks  of  the  rotting  of  the  fruit, 
cold  apparently  being  an  important  factor  in  their  production.  He 
;ilso  found  that  the  addition  of  hydrated  lime  to  soil  in  which  apothecia 
were  developing  prevented  their  maturation. 


Bulletin  383]  BROWN  ROT  OF  APRICOTS  39 

Depleted  Vigor  of  the  Trees  Conducive  to  Monilia  Blossom  Blight 

Trees  attacked  by  such  diseases  as  sour  sap,  bacterial  gummosis 
and  oak  root  fungus  disease  (Armillaria  mellea)  invariably  suffer  the 
worst  from  Monilia  blossom  blight.  The  number  of  infections  in  limbs 
affected  with  bacterial  gummosis  is  frequently  out  of  all  proportion  to 
the  number  of  infections  in  the  rest  of  the  tree.  In  Table  7  the  average 
number  of  infections  in  one  block  is  358  which  is  considerably  in  excess 
of  those  in  the  adjoining  plots.  Several  trees  in  this  plot  were  severely 
diseased  with  bacterial  gummosis,  one  tree  having  552  infections,  most 
of  which  were  confined  to  one  large  limb  affected  with  the  bacterial 
disease. 

Trees  suffering  from  bacterial  gummosis  or  the  other  diseases  men- 
tioned should  be  invigorated  by  proper  treatment.  Trees  in  a  vigorous 
condition  have  a  greater  natural  resistance  to  Monilia  blossom  blight. 

The  Relation  of  Organic  Fertilizers  to  the  Propagation  of  the 

Brown  Eot  Fungus 

Kepeated  isolations  of  fungi  from  chicken,  horse  and  cow  manures 
failed  to  yield  the  brown  rot  fungus,  and  repeated  attempts  to  cultivate 
the  organism  by  planting  spore-covered  mummies  in  them  under  field 
conditions  or  in  bell  jars  at  room  temperature  failed.  Attempts  to 
induce  the  fungus  to  grow  either  on  freshly  cut  or  decaying  alfalfa  or 
any  of  the  commoner  grasses  under  field  conditions  failed.  Apparently 
organic  fertilizers  have  little  to  do  with  the  propagation  of  the  fungus. 

Ornamental  Plants  as  "Carriers"  of  the  Brown  Eot  Fungus 

Of  many  commoner  ornamental  plants  examined,  the  Japanese 
Quince  (Chaenomales  japonica)  was  the  only  one  found  to  suffer  the 
attacks  of  the  brown  rot  fungus,  and  the  fact  that  it  blooms  in  advance 
of  the  apricots  is  significant.  The  twigs  and  blossoms  are  quickly 
killed,  becoming  covered  with  dense  spore  masses  as  they  die.     (Fig.  8.) 

The  fungus  from  the  Japanese  quince  readily  attacks  the  apricot. 
The  fungus  was  easily  recovered  from  lesions  produced  from  sixty 
stab-wound  inoculations  made  with  it.  A  similar  number  of  checks 
remained  sterile. 


40  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION 


FUNGICIDES 

In  the  past  four  years  approximately  one  hundred  distinct  treat- 
ments for  the  control  of  Monilia  blossom  blight  have  been  tried  experi- 
mentally, including  the  use  of  twenty  odd  different  fungicides,  oils, 
coal-tar  derivative  sprays,  proprietary  compounds  and  fungicidal 
dusts. 

Bordeaux  Mixture 

This  fungicide  has  regularly  proved  the  best  for  controlling  the 
disease. 

In  unsanitary  orchards  in  damp  localities  Bordeaux  8-8-50  gives 
better  results  than  Bordeaux  4-4-50.  It  is  not  contended,  however, 
that  the  stronger  mixture  alone  will  effect  a  control.  Striking  instances 
of  control  with  Bordeaux  5-5-50  and  6-6-50  are  given  in  this  paper. 
Satisfactory  control  with  Bordeaux  4-4-50  is  very  rarely  obtained  in 
unsanitary  orchards  in  damp  localities.  Mr.  H.  Owen  of  Haywards 
sprayed  his  orchard  twice  with  Bordeaux  4-4-50  in  1921  at  the  time 
most  favorable  for  the  control  without  even  appreciable  results  from 
the  practical  standpoint. 

Spraying  experiments  to  determine  the  relative  efficacy  of  Bor- 
deaux 8-8-50  and  4-4-50  are  not  complete,  but  the  work  done  thus 
far  indicates  the  superiority  of  the  stronger  mixture. 

One  application  of  either  Bordeaux  8-8-50  or  4-4-50  may  fail  to 
secure  a  practical  control,  but  the  degree  of  relative  control  will  be 
greater  with  the  stronger  mixture.  The  degree  of  control  will  depend 
upon  the  care  with  which  pruning  has  been  done,  the  climate  during 
the  susceptible  period,  and  the  number  of  applications  of  spray  given, 
if  the  case  is  serious  and  the  first  two  factors  are  unfavorable. 

Individual  experience  alone  will  determine  the  proper  strength  of 
Bordeaux  to  use  in  any  locality.  There  is  no  advantage  in  using  the 
stronger  mixture  if  the  weaker  always  proves  satisfactory.  But  those 
growers  who  have  had  no  practical  results  with  one  or  more  applica- 
tions of  Bordeaux  4-4-50  should  not  hesitate  to  increase  the  strength 
of  their  mixture. 

There  is  no  danger  of  burning  either  the  buds  or  the  blossoms  of 
the  apricot  with  a  properly  made  Bordeaux.  As  many  as  five  applica- 
tions of  Bordeaux  8-8-50  were  tried  experimentally  to  large  blocks  of 
trees  in  the  II.  Owen  orchard  at  Haywards  in  1923  without  injury  of 
any  kind.  The  fruit  at  harvest  was  large,  abundant  and  of  excellent 
quality.  In  1922  Mr.  C.  Frost  of  Berryessa  sprayed  four  times  with 
Bordeaux  5-5-50  starting  in  the  red  bud  stage  and  ending  in  the  full 


Bulletin  383]  BROWN  ROT  OF  APRICOTS  41 

bloom.  The  year  was  damp,  and  in  the  same  vicinity  the  disease  was 
very  destructive.  Yet  in  a  block  of  38  trees,  typical  of  Mr.  Frost's 
orchard,  the  average  number  of  infections  was  1.  In  one  corner  of  the 
orchard  where  the  disease  offered  its  greatest  resistance  to  control  the 
average  number  of  infections  per  tree  in  a  block  of  34  trees  was  only  13. 
The  trees  were  seventeen  years  old  and  only  ordinary  pruning  had  been 
given  them.  Mr.  Frost  previously  had  been  unable  to  control  the 
disease  with  a  single  spray,  and  his  losses  were  great.  In  one  season  he 
brought  the  disease  under  control  by  the  multiple  spray  method  with- 
out damage  to  his  trees  or  crop. 

Bordeaux  10-10-50  is  not  infrequently  used,  and  one  grower 
reported  the  use  of  Bordeaux  15-15-50  during  the  full  bloom  without 
damage  of  any  kind.  To  use  Bordeaux  stronger  than  8-8-50  is 
probably  wasteful  and  unnecessary. 

Bordeaux  applied  to  the  open  blossoms  does  not  interfere  with 
pollination  which  probably  takes  place  in  the  case  of  the  apricot  before 
the  blossoms  open.  Experiments  with  new  fungicides  frequently  led  to 
the  burning  of  the  outer  portions  of  the  buds  to  such  an  extent  that 
they  never  opened.  Yet  when  the  burning  had  not  killed  the  reproduc- 
tive parts  within,  these  buds  set  fruit  which  eventually  burst  through 
the  old,  unopened  flower  parts. 

Sulfur-Containing  Compounds 

Sulfur  or  sulfur-containing  compounds  should  not  be  used  on 
apricot  trees,  as  they  are  peculiarly  susceptible  to  injury  by  this 
element. 

Lime-Sulfur  Damage. — Apricot  buds  and  blossoms  may  be  severely 
burned  with  lime-sulfur  fungicides.  High  temperatures  ordinarily 
are  associated  with  this  form  of  injury. 

Besides  burning  the  buds  and  thereby  lowering  the  crop,  lime-sulfur 
(and  other  sulfur-containing  compounds)  frequently  poison  the  trees. 
''Sulfur  poisoning"  was  first  observed  in  this  state  on  apricots  by 
Professor  R.  E.  Smith  of  this  station  in  1915.  The  injury  consists  of 
a  stunting  and  yellowing  of  the  new  growth  and  foliage  and  the 
deterioration  of  the  fruit  which  ripens  late  and  is  distinctly  inferior 
in  color,  size  and  quality. 

In  1921  the  entire  crop  of  apricots  in  the  Deciduous  Fruit  Station 
orchard  had  been  picked  when  the  fruit  in  a  neighboring  orchard  was 
just  commencing  to  ripen.  The  fruit  in  the  station  orchard  was  also 
distinctly  larger  and  of  better  quality.  The  station  orchard  had  been 
sprayed  in  the  red  bud  stage  with  fungicides  containing  no  sulfur 


42  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

while  the  neighboring  orchard  had  been  sprayed  at  the  same  time  with 
lime-sulfur  solution  1-10.  All  other  conditions  in  both  orchards  were 
identical. 

Lime-sulfur  is  rarely  used  now  on  apricots.  Several  years  ago, 
when  it  was  in  general  use,  orchards  sprayed  with  it  could  frequently 
be  told  at  a  glance,  especially  when  some  of  the  trees  had  been  left 
unsprayed  or  else  sprayed  with  fungicides  containing  no  sulfur,  by 
which  a  comparison  could  be  made. 

The  physiological  effect  of  sulfur  on  apricots  is  not  always  constant ; 
young  or  old  trees  in  a  vigorous  condition  may  withstand  its  poisonous 
effects  for  years.  On  the  other  hand,  trees  of  any  age  may  be  so 
seriously  poisoned  by  a  single  application  of  lime-sulfur  that  they 
fail  to  bloom  the  following  year. 

Lime-sulfur  sprays  in  diluted  form  (summer  strength)  may  occa- 
sion very  serious  injury  when  applied  during  the  growing  season. 
Several  trees  at  the  Deciduous  Fruit  Station  were  sprayed  with  lime- 
sulfur  solution  1-30  when  the  fruit  was  very  small.  One  tree  was 
completely  sprayed,  another  was  sprayed  about  the  lower  branches 
only,  and  the  third  on  one  side  only.  The  foliage  turned  yellow  and 
the  fruit  sprayed  with  the  lime-sulfur  virtually  ceased  to  grow.  The 
unsprayed  fruit  developed  normally.  The  fruit  on  the  tree  completely 
sprayed  was  undeveloped  and  green  when  the  main  crop  in  the  orchard 
was  harvested.  The  following  year  the  tree  did  not  produce  a  single 
blossom  and  the  foliage  developed  very  late.  In  1923  the  tree  had 
recovered  and  set  a  normal  crop  of  fruit. 

Effect  of  Pure  Sulfur  on  Ripening  Apricots. — Pure  sulfur  applied 
with  water  may  seriously  injure  ripening  apricots.  An  orchard  at  Los 
Altos  was  sprayed  with  pure  sulfur  at  the  rate  of  10  pounds  to  the 
100  gallons  of  water  on  June  10.  At  the  time  of  spraying  the  fruit 
was  equal  in  size  and  quality  to  any  in  the  adjoining  orchards.  At 
harvest  time  it  was  just  commencing  to  color  when  the  third  or  last 
pickings  were  made  in  the  neighboring  orchards.  The  quality  and  size 
of  the  fruit  was  so  inferior  that  it  passed  at  reduced  price  as  second 
run  fruit  at  the  cannery.  The  following  year  the  orchard  failed  to 
bloom,  but  in  adjoining  orchards  there  was  an  unusually  heavy  setting 
of  fruit.  All  other  conditions  in  the  several  orchards  observed  were 
identical.  Mr.  W.  P.  Hitchings  of  Aromas  sprayed  part  of  his  orchard 
when  the  fruit  was  just  commencing  to  turn  yellow  with  sulfur  at  the 
rate  of  11  pounds  to  the  150  gallons  of  water.  Further  development 
of  the  fruit  ceased  immediately.  The  sprayed  fruit  was  picked  three 
weeks  later  than  the  unsprayed,  and  it  was  distinctly  poorer  in  color, 
quality  and  flavor.    The  foliage  developed  a  sickly  yellow  color. 


Bulletin  383] 


BROWN    ROT    OF    APRICOTS 


43 


Howard  and  Home97  noted  that  self -boiled  lime-sulfur  applied  after 
the  fruit  had  set  caused  it  to  be  stunted  and  the  foliage  to  turn  yellow. 

A  number  of  proprietary  sulfur-containing  compounds  were  used 
experimentally,  but  none  of  them  proved  as  satisfactory  as  Bordeaux 
either  from  the  standpoint  of  disease  control  or  of  the  effects  produced 
on  the  trees. 

Oil  Sprays 

Value  as  Dormant  Sprays. — Oil  sprays  applied  in  winter  for  the 
control  of  insect  pests  frequently  show  fungicidal  properties,  but  in 
badly  diseased  orchards  situated  in  damp  localities  they  generally  fail 
to  control  Monilia  blossom  blight  satisfactorily. 

TABLE  14 
Eesults  Obtained  with  Dormant  Oil  Sprays  in  Private  Orchards 


Orchardist 

Locality 
and  year 

Treatment 

Number  of  sprayed 

trees. 

Age  and  variety. 

Average  number  of 

infections. 

Number  of  unsprayed 

trees. 

Age  and  variety. 

Average  number  of 

infections. 

E.  Snyder 

Aromas, 
1922 

"Ortho"     crude     oil 
emulsion  15-100. 

30  trees  examined. 
18-year  Blenheims. 

109  infections, average. 

Unsprayed. 

6  trees  examined. 
18-year  Blenheims. 
96  infections,  average. 

L.  Carroll. 

San  Jose, 

Balfour-Guthrie 

20  trees  examined. 

1922 

"Dormant  Soluble 
Oil  (miscible  oil) 
10-200. 
Unsprayed. 

35-year  Moorparks. 
235  infections,  average. 

20  trees  examined. 
35-year  Moorparks. 
518  infections,  average. 

F.  McDiarmid. 

Aromas, 

"Ortho"  crude  oil 

30  trees  examined. 

1922 

emulsion  15-100. 

16-year  Blenheims. 
105  infections,  average. 

H.  C.  Smith. 

Hollister, 

"Ortho"  crude  oil 

9  trees  examined. 

1923 

emulsion  15-100. 

16-year  Blenheims. 
676  infections,  average. 

E.  F.  O'Donnell. 

Hollister, 

"Ortho"  crude  oil 

9  trees  examined. 

1923 

emulsion  15-100. 
Unsprayed. 

13-year  Blenheims. 
359  infections,  average. 

9  trees  examined. 
13-year  Blenheims. 
832  infections,  average. 

In  none  of  these  cases  were  results  of  practical  value  obtained. 

While  the  degree  of  control  afforded  by  dormant  sprays  of  oil  is 
usually  very  poor  from  the  practical  standpoint,  occasionally  it  very 
much  reduces  the  amount  of  infection.     This  is  particularly  true  in 


44  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

localities  where  the  climate  is  not  very  favorable  to  the  development 
of  the  disease.  Under  such  conditions  even  a  practical  control  may  be 
obtained  at  times. 

Red  Bud  Oil  Sprays. — A  spray  applied  in  the  spring  just  before 
the  flowers  appear  give  the  best  results  obtainable  with  one  spray.  Oil 
sprays  applied  at  this  time  are  often  extremely  harmful  and  not  to  be 
recommended.  In  1921,  six  plots  of  10  trees  each  in  the  John  Fahey 
orchard  were  sprayed  in  the  red  bud  stage  with  crude  oil  emulsion 
("Ortho"  brand)  30-200  and  distillate  emulsion  ("Spray-mulsion, "  a 
miscible  oil)  15-200.  The  results  were  failures  because  the  sprays 
either  failed  to  check  the  disease  or  burned  the  buds.  Burning  was 
severest  in  the  plots  which  previously  had  been  given  a  dormant  spray 
of  lime-sulfur  1-10.  Both  of  the  oil  sprays  interfered  with  the  pollina- 
tion in  all  the  plots.  Even  the  flowers  which  escaped  burning  failed 
to  set  fruit.  These  results  were  confirmed  by  duplicate  experiments 
made  by  Mr.  Tocher,  farm  advisor  at  Hollister,  in  the  B.  Jensen 
orchard  in  1922.  His  red  bud  spray  of  crude  oil  emulsion  ("Buggo") 
30-200  not  only  burned  many  of  the  buds  and  interfered  with  the 
pollination  of  the  flowers,  but  it  also  failed  to  adequately  control  the 
disease.  His  unsprayed  trees  averaged  573  infections  per  tree  and  his 
sprayed  trees  473. 

It  is  believed  by  many  that  oil  sprays  inhibit  the  production  of 
spore  pustules  on  the  blighted  twigs  by  virtue  of  filling  the  pores  and 
interstices  of  the  bark  with  oil,  thereby  preventing  the  penetration  of 
rain  water  into  the  wood  necessary  to  the  reactivation  of  the  fungus. 
Spore  production  may  be  delayed  somewhat  by  the  coating  of  oil  on 
the  bark,  but  in  wet  seasons  spores  are  eventually  produced  in  spite 
of  it. 

The  fact  that  oil  sprays  generally  fail  to  control  the  disease  should 
not  prejudice  growers  against  them  or  militate  against  their  use  in 
the  field  for  which  they  are  primarily  intended — the  control  of  insects. 

Fungicidal  Dusts 

Dusting,  theoretically,  is  the  ideal  means  of  controlling  disease  and 
insect  pests,  since  the  equipment  is  light  and  may  be  used  on  steep 
hillsides  or  boggy  ground  unfavorable  to  the  use  of  liquid  spray  rigs. 
Also,  dusting  is  considerably  cheaper  than  liquid  spraying  and  much 
more  quickly  done. 

Experimental  Dusting  for  the  Control  of  the  Disease. — All  the 
better  known  fungicidal  dusts  tested  in  various  parts  of  Santa  Clara 
County  proved  very  unsatisfactory.     Ten  trees  and  upwards  were 


Bulletin  383]  BROWN  ROT  OF  APRICOTS  45 

included  in  the  dusted  and  in  the  check  plots.  The  check  plots  always 
adjoined  the  dusted  plots  on  the  windward  side.  Dusting  was  done  late 
at  night  by  artificial  light  or  before  sunrise  to  avoid  the  interference 
of  winds. 

In  mature  trees  of  average  size  the  number  of  infections  invariably 
exceeded  one  hundred  per  tree.  Even  the  degree  of  relative  control 
was  slight,  and  in  some  instances  as  many  infections  developed  in 
dusted  trees  as  in  check  trees.  All  of  the  materials  were  tried  at  least 
once  in  the  red  bud  stage,  and  frequently  as  many  as  three  dustings 
were  given  at  different  times  during  the  bloom.  Under  similar  con- 
ditions liquid  sprays  of  standard  fungicides  gave  far  better  results. 
The  following  materials  were  used : 

1.  Commercial  Bordeaux  Dust  (General  Chemical  Co.). 

2.  Dry  Lime  Sulfur  Dust  (Sherwin-Williams  Co.). 

3.  Lime  and  Sulfur  Dust  (25  lbs.  air-slaked  lime  and  65  lbs.  ventilated 

sulfur ) . 

4.  Lime    and    Dehydrated    Copper    Sulfate   Dust    (5%    dehydrated 

CuS04  and  95%  hydrated  lime). 

5.  Lime  and   Dehydrated   Copper   Sulfate   Dust    (10%    dehydrated 

CuS04  and  90%  lime). 

6.  Barium-Tetra-Sulfide  and  Calcium  Casemate  Dust  (93%  "B.T.S." 

and  7%  "K-Seen")   (Balbour-Guthrie  Co.). 

7.  Kaolin  and  Dehydrated  Copper  Sulfate  Dust    (5%   dehydrated 

CuS04  and  95%  kaolin.     Made  into  a  paste  with  water,  dried 
and  ground.) 

8.  Kaolin  and  Dehydrated  Copper   Sulfate  Dust    (4%   dehydrated 

CuS04  and  96%  kaolin). 

9.  Lime  and   Dehydrated   Copper   Sulfate  Dust    (20%    dehydrated 

CuS04  and  80%  hydrated  lime). 

10.  Lime  and  Dehydrated   Copper   Sulfate   Dust    (30%    dehydrated 

CuS04  and  70%  hydrated  lime). 

11.  Copper  Sulphosteatite  Dust   (10%  dehydrated  CuS04  and  90% 

talc  made  into  a  paste  with  water,  dried  and  ground). 

12.  Coper   Sulphosteatite  Dust    (20%    dehydrated   CuS04  and  80% 

talc  made  into  a  paste  with  water,  dried  and  ground). 

13.  Talc  and   Copper   Carbonate  Dust    (20%   copper  carbonate  and 

80%  talc). 

The  last  five  dusts  were  tested  in  the  orchards  belonging  to  Messrs. 
J.  Lewis  and  E.  F.  O'Donnell  at  Hollister  in  1924.  The  dusted  blocks 
contained  from  eighteen  to  twenty  trees  each,  and  each  block  was 
dusted  three  times,  the  first  dusting  being  given  when  the  red  buds 
were  cracking,  the  second  when  half  the  blossoms  were  out  and  the 


46  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

third  when  the  trees  were  in  full  bloom.  Plots  of  fourteen  to  twenty 
trees  immediately  adjoining  the  dusted  plots  were  sprayed  once  with 
Bordeaux  5-5-50  and  6-6-50.  All  other  conditions  were  identical. 
From  three  to  eight  times  as  many  infections  were  counted  in  the 
dusted  plots  as  in  the  sprayed  plots. 

Ten  or  more  duplicate  experiments  with  the  10%  dehydrated  cop- 
per sulfate  and  lime  dust  were  made  by  farm  advisors  in  several 
counties.  The  dust  was  applied  in  single  or  multiple  applications  start- 
ing with  the  red  bud  stage  and  ending  with  the  full  bloom.  No  note- 
worthy control  was  obtained  except  in  one  instance  and  this  in  an 
orchard  relatively  free  from  the  disease  even  on  the  check  trees.  In 
general  the  number  of  infections  closely  approximated  those  on  the 
check  trees. 

Results  Obtained  with  Fungicidal  Dusts  in  Private  Orchards. — At 
Haywards  in  1922,  Mr.  H.  Owen  dusted  a  block  of  five  trees  six  times 
with  10%  dehydrated  copper  sulfate  and  lime  dust  between  the  red 
bud  stage  and  the  full  bloom.  The  results  were  of  no  value,  there 
being  an  average  of  283  infections  to  the  tree.  In  another  part  of  his 
orchard  Mr.  Owen  applied  the  same  dust  at  least  twelve  times  to  one 
tree  with  no  better  results. 

No  fungicidal  dust  used  in  the  experiments  has  proved  as  efficaceous 
as  liquid  Bordeaux,  even  multiple  dusting  failing  to  do  the  work  of 
one  liquid  spray. 


WHEN  TO  SPEAY  FOR  MONILIA  BLOSSOM  BLIGHT  CONTROL 

In  general  it  may  be  said  that  in  orchards  not  yet  seriously  diseased, 
even  if  situated  in  regions  where  the  disease  has  already  proved  severe 
in  other  orchards,  or  in  orchards  situated  in  regions  where  the  disease 
never  becomes  a  serious  problem  because  climatic  conditions  are 
normally  unfavorable  to  it,  an  application  of  Bordeaux  8-8-50  to  the 
red  buds  or  even  a  little  later  when  the  red  buds  are  cracking  and 
show  the  folded  white  petals  beneath  the  red  sepals  ordinarily  gives  a 
thoroughly  satisfactory  control.  Even  Bordeaux  5-5-50  or  6-6-50 
frequently  give  satisfactory  results  under  these  conditions. 

If  the  size  of  the  orchard  or  the  spraying  facilities  at  hand  are 
such  that  all  the  trees  cannot  be  covered  when  the  red  buds  are  crack- 
ing, a  period  usually  of  short  duration,  or  if  there  is  reason  to  believe 
from  official  weather  forecastings  that  this  period  will  be  marked  with 
storms,  spraying  operations  should  be  advanced  a  little.  It  is  better 
to  atari  a  little  early  rather  than  a  little  too  late. 


Bulletin  383]  brown  rot  of  apricots  47 

In  badly  diseased  orchards  where  climatic  conditions  and  the 
unsanitary  conditions  of  the  trees  render  control  with  a  single  spray 
difficult  or  uncertain,  multiple  spraying-  should  be  employed.  Several 
applications  of  Bordeaux  8-8-50  should  be  given  in  quick  succession, 
starting  at  the  red  bud  stage  and  stopping  when  the  trees  are  in  full 
bloom  or  even  a  little  later  when  the  petals  have  been  shed. 

It  is  impossible  to  state  just  how  many  days  apart  these  sprays 
should  come  because  the  temperature  affects  the  rate  at  which  the 
blossoms  open.  Nor  can  the  exact  number  of  applications  of  spray 
necessary  to  secure  a  practical  control  of  the  disease  be  given.  The 
grower  must  determine  this  for  his  own  individual  locality.  Some 
localities  require  but  one  spray,  others  two,  three  or  more.  This  point 
will  be  determined  largely  also  by  the  extent  to  which  careful  pruning 
has  been  practiced  in  the  orchard. 

When  but  two  sprays  are  to  be  given  they  should  come  at  the  red 
bud  stage  and  the  first  part  of  the  bloom  rather  than  at  the  last. 

Multiple  spraying  of  seriously  diseased  orchards  should  be  prac- 
ticed until  the  disease  has  been  brought  under  control.  Then  one  spray 
may  hold  the  disease  within  the  limits  of  practical  control.  Individual 
experience  alone  will  determine  this.  It  is  being  done  today  in  many 
orchards  where  the  disease  was  once  a  very  serious  problem.  Certainly 
no  attempt  to  revert  to  the  single  spray  method  or  to  reduce  the 
strength  of  the  Bordeaux  should  be  made  until  a  highly  sanitary 
condition  again  prevails  in  the  orchard. 


THE  PEEPAEATION  OF  BOEDEAUX  MIXTUEE 

There  are  several  ways  of  making  Bordeaux  mixture,  but  possibly 
the  so-called  "stock  solution  method"  offers  the  greatest  convenience. 

Preparation  of  the  Stock  Solutions 

To  make  the  stock  solutions  proceed  as  follows :  Very  carefully 
determine  the  40-gallon  level  of  two  or  more  ordinary,  clean,  wooden, 
water-tight  barrels  and  mark  with  copper  tack  or  wooden  peg.  Empty 
the  barrels. 

Suspend  80  pounds  of  copper  sulfate  (Milestone,  blue  vitrol)  in  a 
clean  gunny  sack  in  one  of  these  barrels  and  fill  with  clean  water  to 
the  40-gallon  level.  The  water  may  be  cold,  but  warm  water  is  better, 
and  hot  water  still  better.  If  the  water  is  very  cold  several  days  may 
elapse  before  all  the  bluestone  is  dissolved,  but  if  sufficient  hot  water 


48  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

is  added  to  take  off  the  chill,  the  bluestone  ordinarily  will  dissolve 
during  a  night.  In  very  warm  water  it  dissolves  in  a  few  minutes. 
Thus  40-gallons  of  stock  solution  are  made,  each  gallon  of  which 
contains  two  pounds  of  bluestone.  Never  prepare  the  bluestone  stock 
solution  in  iron  barrels  as  it  will  destroy  them. 

In  a  second  barrel,  the  40-gallon  level  of  which  previously  has  been 
determined,  dump  80  pounds  of  freshly  burnt  lime  (unslaked,  lump  or 
fat  lime)  and  add  enough  water  (hot  or  cold)  to  cover.  Additional 
water  must  be  added  after  the  mixture  starts  to  boil  to  prevent  drying 
out  and  burning.  But  too  much  water  must  not  be  added  at  any  one 
time  or  the  lime  may  not  slake  properly.  Stir  only  occasionally  to  per- 
mit water  to  reach  all  parts  of  the  mass.  Violent  stirring  tends  to  cool 
the  mixture  which  is  undesirable  until  the  reaction  is  complete.  After 
the  lime  is  slaked  add  more  water  until  the  40-gallon  level  is  reached. 
Stir  until  all  the  paste  or  lumpy  substances  in  the  bottom  of  the  barrel 
are  broken  up  and  a  smooth  "milk  of  lime"  obtained.  The  barrel 
now  contains  40-gallons  of  stock  lime  solution,  each  gallon  of  which 
contains  two  pounds  of  lime.  Never  use  old  lime  that  has  become  air- 
slaked  and  turned  to  powder  as  it  contains  inert  chemical  substances 
unsuited  to  the  making  of  a  good  spray. 

This  constitutes  the  preparation  of  the  stock  solutions.  They  will 
keep  indefinitely. 

How  to  Mix  the  Spray 

Fill  the  spray  tank  one-half  to  two-thirds  full  of  clean  water,  start 
the  agitator  working  and  pour  the  necessary  amount  of  bluestone  stock 
solution,  previously  determined,  into  the  tank  through  the  sieve.  Next 
slowly  pour  in  the  required  amount  of  stock  lime  solution  through  the 
sieve,  breaking  up  any  small  pellets  of  lime  with  a  flat  paddle  or  the 
gloved  hand.  Actual  grit  or  other  impurities  left  behind  in  the  sieve 
should  be  thrown  away.  Always  thoroughly  stir  the  stock  lime  solu- 
tion before  drawing  off  as  it  tends  to  settle.  Fill  any  space  that  may 
be  left  in  the  tank  with  water  and  proceed  to  spray  the  trees.  Do  not 
stop  the  agitator  at  any  time  after  starting  to  mix  the  spray  unless 
absolutely  necessary. 

The  two  concentrated  stock  solutions  should  never  be  mixed  before 
diluting  with  water,  especially  when  the  stock  solutions  are  hot,  or  a 
poor  Bordeaux  will  result.  The  cold  water  placed  in  the  tank  first  will 
sufficiently  cool  and  dilute  freshly  made  stock  solutions  to  prevent 
undesirable  reactions  from  taking  place.  Also  the  bluestone  stock 
sol  n1  ion  should  be  added  to  the  water  first,  and  the  lime  last. 


Bulletin  383]  BROWN  ROT  OF  APRICOTS  49 

An  example  of  how  the  stock  solutions  are  used  in  actual  practice 
may  be  given :  To  make  a  200-gallon  tank  of  Bordeaux  8-8-50,  sixteen 
gallons  of  bluestone  stock  solution  and  sixteen  gallons  of  the  lime  stock 
solution  should  be  added  in  the  way  described  and  the  tank  filled  to 
the  200-gallon  level,  as  in  Bordeaux  8-8-50,  each  50  gallons  contains 
8  pounds  of  bluestone,  200  gallons  requires  32  pounds.  Since  each 
gallon  of  stock  solution  contains  2  pounds  of  bluestone,  16  gallons  of 
the  stock  solution  will  supply  the  requisite  32  pounds.  The  same  is 
true  of  the  stock  lime  solution. 

Some  growers  prefer  to  make  their  stock  solutions  of  lime  and  blue- 
stone  in  a  one-to-one  ratio  instead  of  in  the  two-to-one  ratio,  that  is  by 
dissolving  1  pound  of  bluestone  or  1  pound  of  the  lime  to  each  gallon 
of  solution  instead  of  2  pounds.  There  is  no  objection  to  this  method 
except  that  it  requires  twice  as  many  barrels  to  hold  the  stock  solutions. 

A  three-to-one  ratio  bluestone  stock  solution  may  be  made  with  very 
hot  water,  but  it  must  be  used  up  before  it  has  cooled,  because  when 
cold  the  solution  becomes  supersaturated  and  some  of  the  bluestone  will 
settle  out,  thus  upsetting  the  ratio.  A  three-to-one  stock  lime  solution 
is  impractical  as  the  mixture  is  too  thick  and  plaster-like  to  be  handled 
easily. 

While  stock  solutions  once  prepared  keep  indefinitely,  the  spray 
made  from  them  should  be  used  at  once.  The  best  adhesive  and 
fungicidal  properties  are  always  obtained  when  the  spray  is  freshly 
prepared. 

The  level  of  any  stock  solution  left  over  at  the  end  of  the  spray 
season  should  be  marked  in  the  barrel  with  a  copper  tack  or  wooden 
peg  in  order  that  the  water  lost  by  evaporation  may  be  replaced  with 
accuracy  before  using  next  year. 

Commercially  Prepared  Bordeaux  Sprays 

Home-made  Bordeaux  mixture  is  much  cheaper  than  any  of  the 
commercial  products  on  the  market  today  and,  when  properly  pre- 
pared, is  equal  to  any  and  superior  to  most  of  them  in  its  adhesive  and 
fungicidal  properties.  Growers  are  therefore  urged  to  familiarize 
themselves  with  the  preparation  of  this  well  known  spray. 


50  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


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